I think you could do it, BUT, it depends very much on the cat. I'm pretty sure you would not be able to give Fister a pill, or give him any kind of injections. It would take two of you.

However, the cat I'm catsiting now, is easier to handle than Fister was a few years ago. So far, I've been able to clip 6 of his nails - one more day to go.

Whatever you decide to do, I would make sure to have some kind of insurance if anything happened (not only concerning medicine), and to give the cat medicine a few times with the owner present.

Good luck!