I agree,.. if it was majid, there would be all sorts of etch-a-sketch type drawings to accompany an explanation that would involve unraveling your socks, and using the strands to knit some sort of auto-locking ascender.
Standard SAR stuff of course,

Not any more it isn't. aceto = majid_sabet. I am 100% certain of this. Or did you pretty much already figure that out?

Easiest way is I think to lower the rescuer.
Use a munter hitch for that and connect the ropes with a edk.
The edk passes through the munter.

... you can rap down to them and then reach the ground, but you will need to do at least one knot bypass in order to get them down. ... The rescuer will be at the top of the cliff on the exit point with what ever gear is needed.

[opinion]

A Load Releasable Hitch - Mariner knot - is a tool that is often used in rescue applications because it provides redundant control. I think people are confused with the mule knot methodology and how it would be employed in this situation.

Passing a knot is passing a knot regardless of the situation.

Runnit, you already answered the question in your post. Your mention of using a 6mm chord makes you uncomfortable. Why are you not then using an 8mm chord instead? My knowledge of rescue systems is a bit rusted, having not used them for some time, but it seems prudent to maintain the beefieness and overkill that is found throughout the SAR communities in the US. I assume that you already understand and practice the standard method of passing a knot under tension. Why not then beef up your system to be stronger?

Also, if you are in that situation, it might be easier and better controlled if you were lowered into the scene, leaving the knot passing to a belay crew at the top of the cliff. This would allow you to maintain control of your victim and allow you to have two hands free to attend to thier needs.

[/opinion]

Um, really?!?

Now that would be fun to watch...

Um, really?!?

Wow, I'm gonna go try that, could be really useful!

as you want to pass a knot while rapelling this is a possibility (using a long cord with a munter muleand a prussik)

...
It's impossible to use that technique to pass the knot on a weighted rope, obviously.

sorry but that's wrong. (at least as long as we're talkin aout lowering someone)
It works that way.

Yes it might be problem depending on the weight of the bodies and the ropes diameters.
Fatter ropes are easier to control in my opinion.

as you want to pass a knot while rapelling this is a possibility (using a long cord with a munter muleand a prussik)

This is getting way to complicated.
Simple is safer.

You're telling me

Anyway, thanks to everyone for the (on topic) replies. It's been an interesting bit of research.

Based on everything I've been able to gather from a range of sources, I've got 3 different solutions that I'd be happy to play with depending on the situation.

A.
If we have radios, the most experienced person stays up the top and lowers someone else tied into the end of the rope (like lowering a top belay) down to the casualty so the knot bypassing can be taken care of from the top of the cliff and the rescuer just has to connect the casualty and help them down. Comms between the rescuer and the top is essential.

B.
If the casualty isn't badly hurt and can help out, the rescuer raps down and ties off, sets up a belay on the rescue line and lowers the casualty on the end of the rope, taking care of the bypasses from where he's hanging as he lowers. That way he's only got to deal with the weight/complications of one person at a time. The casualty will have to be able to fend off the wall themselves and sort themselves out at the bottom (ideally having someone else meet them down there).

C.
Worst case, the rescuer raps down to the casualty and lowers with them. I'm thinking the best way to manage all of the different attachments is to use one biner/figure 8 as the focal pt which everything else gets attached to (cow tails, belay devices, prussics etc). The casualty would be attached by girth hitching a sling from each shoulder and connecting them with a biner (that would then be clipped into the focal pt) so they naturally sit in their parachute harness.

To bypass the knots, stop rapping a couple metres above the knot, fix a sling above the belay device with an autoblock, tie a figure 8 on a bite below the knot and connect it to the tails of the autoblock. Connect a 2nd device below the knot to the focal pt and rap down the slack between the sling and the knot until the 2nd belay is loaded up. This saves stuffing around with prussics and I think that it's easier to make sure you're always correctly attached to the rope.

If I did have to use a prussic for some reason, I'd attach it to the rope above the 1st belay device and tie a munter-mule to the focal pt to lower on to the 2nd device. I'd definitely have a back up figure 8 on a bite below the 2nd device too, but connecting the back up to focal pt gets a bit messy and means you've got the potential for shock loading with metal on metal (biner on focal pt).

Using an autoblock off your leg loop as a back up brake is a given.

Thoughts?

Now I've got a plan, hopefully i won't need to use it this weekend.

BJ