In reply to Flashy:
Lots of good advice about mechanical devices above.
My 2P. If you go down the mech device route practice on icy ropes, not all toothed devices are useable and from personal experience when it slides it is frightening... Petzl devices are as good as any IMHO.
For the knot option, try different knots and varying diameter cord. I have tried them all and have yet to be impressed by any other than a standard prussik with two or three wraps or the French prussik for abseil protection.
Moving a standard prussik up the rope is easy when one realises it has to be first unweighted and loosened slightly. A quick push with the thumb on the back loop should be second nature.
Again from personal experience, getting an unharnessed victim out of a crevasse is unlikely to be carried out by a heavy person. Crevasses often taper wickedly and the victim is likely to be crushed tight. If (when) I am ever daft enough to solo travel on a glacier I at least put on a harness and hope any rescue party has a long clip stick.