My favorite tactic for when there's someone around like that is simply to *enlist* them. (and this goes for people being bored and/or distracting to your subjects) It doesn't have to be a big deal, but a lot of people will actually enjoy following your lead if they feel like they're suddenly part of a team. (And a lot of the rest will tend to try and escape the sudden responsibility, either way, you get your shots and they're not in your way, or worse, competing with what you're trying to do cause it's turned into something about pride.)
If you're shooting a wedding, you're kind of in the festivities business, in a way, never hurts if people are having fun around you. If they *like* you, feel good around you, they'll be that much more likely to want to pass your name around, etc, etc, too.
Especially when you're kind of confined to doing the obligatory, standard stuff, there's almost always another angle or even a bunch of reaction shots you can hint to someone else about but can't go get yourself. Good way to get someone on your side, early.
It's kind of more fun to be the backup than the pro, anyway, (Got started upstaging pros, myself) ...so show em the fun.
The last wedding I went to as a guest was actually kind of fun: a lot of the guests were art photographers, one of whom was officially-tasked with actually shooting the wedding: their first time ever. I kind of got to be the *helpful* old salt on the scene, just doing some black and white.