I've stored crushed grain up to 6 weeks double bagged in giant ziploc bags. Its probably not the most ideal situation but I didn't have any negative side affects.
My first AG which was Bee Cave Haus Pale Ale, the crushed grains sat in the fridge sealed in a bag for a month, then sat in a SS pot unsealed with the lid on for well over another month before I got to brew it. Best beer I ever brewed.
Put it in the freezer, preferably in a vacuum-sealed bag. I don't know how long it'll keep that way, but it's your best shot, short of brewing it all up over the next couple of weeks.