get some jumbo or at the very least gallon sized ziplock bags. get a couple people and portion out the larger package into smaller ones as quick as you can. make sure to remove as much air as you can w/o crushing the buns when sealing the bags. you could also try getting ahold of some O2 absorbers to toss into the ziplock bags. that way, except for the initial separation, you only expose the buns to air a few at a time.
All Weber, All Charcoal-18.5" Kettle, Go Anywhere, Performer, 18.5" WSM, NYG Smokey Joe