do you have a tape-label maker?

this peel-apart tape works well IMO. the lab techs at school do this same trick as well.

unpeel a bit (1" or so) and stick it in the canister, sticky side down(toward the spindle). then wind the film in the same direction, causing it to stick to the tape.

I've done this 'use the same roll in different cameras' many times before, such as testing out point and shoot cameras without shooting a whole roll, etc...

just put your lenscap on, and shoot until you've gone 2 or 3 frames past the last frame you were on in your F5. its worked for me every time.

re:spacing, I've found my friend's EOS-1N's and my F100 have almost identical spacing. think of neg pages, they need to be almost identical to fit properly, etc...