You know, this maybe quite a stretch, but maybe with a little imagination, you might be able to keep the other cat out of one box. Some pet supply companies sell pet doors that are activated by a collar that the pet wears. If you could maybe find a hooded litter box and pet door of about the same size.....It may work. I have only one cat and have never tried this, it was totally an idea that just came to me. I think its because it would kill me if I had to give up my own cat.
Also, beware of people who take free pets for research. You might try a cat rescue organization, they are not for profit and no kill organizations, and a good way to make sure your pet ends up in a good loving home.

Good luck whatever the outcome.