Have they done x-rays on him yet? The x-rays should show what is inside of him or at least give them an idea. My girlfriends cat Tuna had surgery to remove a plastic curtain pull that was stuck in his instestines, he did just fine after the surgery. To this day he's still as naughty as ever.

http://www.petoftheday.com/talk/show...light=tuna+vet

editied to at this thread which was right after Tuna's surgery.
http://www.petoftheday.com/talk/show...light=tuna+vet