I used to load cassettes years ago from bulk rolls. In the darkroom I had two nails in a piece of wood exactly 62" long which is the length of a 36 exp film. I also had a pair is scissors and an empty cassette opened ready with tape on the centre of the spool ready to take the film.

Hook the sprocket of the open end of the film over one of the nails and run the film up to the other nail and pop one of the sprockets over the other nail. That stops the cut film from curling up and possibly getting dusty. Use a pair of scissors to snip off the remainder of the roll and put it back in the tin. The bit you have cut off can then be wound onto the empty cassette in your own time with the remainder out of harms way.