Daniel, I don't have the answer, but I do feel for you. My problem didn't involve pills (and I took them for weeks before my addiction became active without having any very memorable problem getting off of them), but I still ask myself the same question. It's a precarious place to be in for all of us. For you, I'm just hoping that this surgery helps enough that you won't need them later. NA includes a clause for legitimate medical reasons, but it's obviously something to be taken very seriously by any addict. Talking to your doctor and especially a sponsor (if you have one) or other people at meetings (if you go to meetings) sounds like a good idea.
Penny...I'm in the middle of watching that exact episode right now!