I'd say just quickly jumping up and then back down would make you seem rather suspicious if a FA does see it ... what I always do is just have a nice chat with the FA's (without camera in hand yet) about how long they've been with the airline, etc. After that, then ask "hey, would it be ok if I went and got my camera to take a shot really quick?". They always say yes when done that way. I've had several QANTAS crews in on the photo taking (they are especially fun FA's normally), having pax sit down and having fun with my camera themselves too. It was great. That same way of doing things works with getting free inflight snack packs, etc.
Also works with getting into the cockpit for the coveted heavy jet cockpit shots. Always works for basically everything while flying. Of course, I always milk the "pilot in training" line too, that helps some.
Best wishes in your adventure to get cabin shots, they might be boring--yes, I agree--but they sure as hell get you to the front page!