I wrap items in paper. It is possible the exact amount of bedding an item needs is the exact amount of newspaper required to wrap it. I would use newspaper or brown paper bags. Maybe if you leave a paper lunch bag open on top for donations and then close it and replace with a new one the next day. You can also cover the bin with material like a shear curtain. Fruit flys seem to like to congregate on computer screens. This would annoy coworkers. You might have a wrap in newspaper policy, wrap like a fish :-). Like the lady that had a bin at a library for children you might need to after work "unfeed" the worms and bring that material home to another group of worms. Better yet if you could get coworkers to wrap in newspaper and then drop thier donations into a paper bag.