Aragorn shakes his head.  "I never trained with the bow."

He's several times wished he did, but when he was young, the Elves were all so much better than him that he didn't have the dedication to get really good at it.

"And your plan...  It would work if they didn't know the Ring was here.  With it...  it might work."  He holds up his hand in salute.  "We will be in the hollow down there when you return, most likely.  Good luck."

The only alternative is to run away and abandon these people to their fate. Gord isn't exactly decided on risking his life for their sake, but putting down a bunch of wraiths is risking one's life for the sake of everyone in the world.

Nondetection. He doesn't think it will help but now's not the time to be stingy with resources. Disguise self, in case some of the wraiths get away and bear a grudge. And he takes off running downhill; he doesn't have time to be maximally stealthy all the way and he's hoping they can't actually see him while he's far enough away, horses or no horses.

Can he approach them stealthily to where it'd take him five minutes to close the distance running, without them seeming to notice, while actually being in a tearing hurry?

Well, how far does he want to go out of his way?

If he sets out down the side of the hill where the hobbits and Strider came up, he'll quickly find a hidden path leading back towards the front face of the hill (toward the Road where the... six wraiths, now... are sitting on their horses) some of the way down.

But only some of the way.  By about halfway down, he'll be more in the open with only bushes for cover.

Gord needs to get to them while it's daylight. 

He can go invisible for eight minutes but he doesn't know if it will help; Golarion wraiths can sense living creatures nearby. The invisibility could also work for a getaway, if he needs one later and can get out of their live-creature-sensing range.

...if they can fly faster than he can run, and his channels don't work and they end up chasing him, then he's fucked. But channels only harm undead, so he doesn't have to check if they're really wraiths before using them, and it really ought to be enough. He could just approach them openly and then channel at the last moment, but they might ride away if they see him coming. (He really hopes they can't fly.)

So, he'll try to approach them as stealthily as he can without risking it being dark before he reaches them - if they can only see at a distance using their horses then this might actually work? - and then, if they let him get close enough, cast invisibility and minute buffs and close the rest of the distance.

This isn't a great plan but it's the best one he's got. None of his defensive abilities or resources work against incorporeal undead; turtling up on the hill went out the window the moment wraiths came into play.

The wraiths must have split up while he was on the way down - there're only four of them there before he gets close.

One of them seems to be facing (for what it's worth) in his general direction, but he hasn't moved recently.  In fact, none of them have moved at all, nor have their horses except for the slight wind blowing their cloaks and manes.

So if they have sensed him, they're not giving any signs of it.

If two of them already split off (and where did they go so quickly, the horses surely can't fly) and another three are unaccounted for, then most of them might strike at the hill-top while these four draw him off. 

...but they won't strike until it's dark, and this is still his only chance to take out some of them in relative safety. It wouldn't help anything if he turned back now. (He does check whether Strider is desperately waving for him to come back from the top of the hill.)

So he closes to a few minutes' running distance, ducks into the best cover he can find at that range - some bushes that might at least obscure his casting - and casts invisibility, protection from evil, remove fear, and runs towards them at a slight angle, as if to pass them from the right. 

Do they track his movement, or do anything else?

They might not see him... but the Ringwraiths can smell a Man running toward them.  He doesn't smell like a Ranger, or one of the natives of Bree, but he's most likely a Man.

A moment after he starts running, the closest wraith shrieks a piercing cry, one that they know will put fear into the hearts of all but the bravest of Men or Halflings.

But to their surprise, he keeps running without fear!  Two of the wraiths gallop toward him.

That's a problem; he wants to catch all four of them in a channel.

A dire wolf appears, as large as one of the horses. It stalks towards them with menacingly, growling, not breaking out into a full run so as not to scatter them. Do they turn back?

They... draw rein at the suddenly-appearing wolf.  It doesn't smell like any wolf or warg they've smelled before, but it's pretty clearly a wolf!

One of them circles around, to try to cut off his retreat should he retreat.

The other hisses at the wolf in Black Speech, in case it can understand, with magic to make his words convincing:  "Kill the man!"

Gord's Comprehend is still up so he catches that. Do the wraiths have magic to command beasts, but no detect magic to see that they're summoned ones?

Aaargh, they're so close, the other two wraiths are just a couple of minutes away. He needs to make these ones think he's enough of a threat to make them regroup, or call the others to help them, but if he channels they might just scatter.

Would making them scatter, and only wounding or (at best) downing two wraiths, be a victory? A victory here is making them afraid to attack tonight. Gord will be better prepared tomorrow.

Getting only two of them... doesn't feel like a victory, not one that'd make the other four too frightened to attack during the night.

It's unclear how much good the invisibility is even doing him, at this point. Gord casts Lesser Mirror Image, runs towards the closest rider, and tries to hit it with his sword, like the dumbest charge out of stories.

The wolf is going to prevent the other rider (or at least its horse) from interfering with this, or running off.