You could look at one of those "Experience" gifts - I think they cover all sorts of things, so not just racing a car round Silverstone or skydiving or other "extreme" activities. Hotel stays, dinners, theatre, train journeys (eg orient express type short lunch trips (in England) etc. There might be something there that would suit him? (Trouble is you might have to buy for 2 so he wouldn't be going on his own).
It could be something to look forward to when he has recovered from surgery, but you still have something (a voucher with info) to hand him on the day.
Puzzles, jigsaws to occupy him whilst convalescing?