Actually that's exactly how billmelater works. On several websites it's beside the credit card payment form. Unfortunately I can't think of an example site off the top of my head.
I see it on ecommerce sites all the time. It's on NewEgg for example last I checked. It's very common.
Logn is correct, it work exactly like this. Performance Bicycle uses it, eCost.com, and Drs. Foster and Smith. I think I've seen it for flowers as well.