Hey Adam,
Nope, there's no way to restrict coupons to a single use presently, either in the API or on Etsy proper, and probably not in the near future. It's something we've discussed though, glad to hear it echoed as potentially useful.
One thing we'll hopefully get to you soon, though, is use counts for a coupon in the API. Once we've got that, you should be able to poll and update your coupons as necessary. You could also do this now with the receipts resource and the coupon association upon it, although it would be a bit more onerous.
One thing to note in any case, though, is that you're currently limited to only 100 active coupons. If you're planning on having many "single use" coupons, that won't work.
Hope this helps!
-Chris