I don't really remember how the commissary shows up when you purchase there (its been years and I'm too lazy to dig through my statements), but I'm fairly sure it comes through as grocery & I'm also fairly sure they sell gift cards there. You might look at that avenue with some grocery focused cards, instead of the base/mil STAR, etc. cards.

As an aside, I'd be cautious with large purchases on base. There's no good reason it should make your life difficult, but it could definitely be a brow-raiser for your command, if they for w/e reason, hear about it. Just because there's not a regulation against it (that I know of) doesn't mean someone won't make a fuss about it. Purely my thoughts on the matter, take em or leave em.