Is there any way to do this? Has anyone come up with a method? (preferably something that doesn't require wearing a watch or band).

wearing a "ring" if that helps any.

Backpalming a pen is difficult (unless you are doing a goshman pinch type motion with the clip). However, in terms of doing it to hide or produce the pen, Rune Klan has an EXCELLENT routine that starts of with a smart idea for "backpalming" a pen in his fantastic book Rune's World.

(I've gotten more usable material from that book from almost anything else).

http://www.penguinmagic.com/p/S12255

Not so much a back palm, but how about using the old matchstick vanish to accomplish this? Modifying this principle and watching your angles could work. Bizzaro has a CD-ROM filled with ideas for Sharpies called "A Marked Man". You could tweak some of his ideas to fit your needs. Just some thoughts...

you could backpalm a sharpie alot easier than a pen,check out magic with markers by byrd and coats