It will take you a while since you can only do four at a time, but you could always buy the penny after rebate paper reams. You'd also have to pay tax of course, but you'd only be losing ~5% vs 13%. If you have no use for the paper, just donate it to a school & you can probably get a tax write off.

Or just float the $600 and wait to buy something you actually need. They've got a bunch of random things on the website (not just office stuff). I bought some free weights there a couple months ago with some expiring rewards & they price matched to Amazon.