When I shot bulk film, I used a film changing bag for loading the film loader and such. They're very handy to have around just for situations like yours. You open the zipper, put what you want to work with inside, close the zipper and stick your arms up to the elbow in the cuffs. There is elastic around the cuffs and the material is like a rubberized cloth so it's light-tight. You can pop the end off the film cassette (if it's a standard 35mm cassette) with a bottle opener. If you do it carefully, it won't get bent up. Pull the spool out of the cassette, find the end of the leader, slip that through the slot in the cassette as you slide the spool back in the cassette. Snap the end back on and you're done. Here's a link as an example but you can probably find cheaper ones on E-Bay or Amazon.
Film Changing Bag