The only commercial product I've ever seen (and apparently caught very little traction, even in California) were these:

http://www.microfueler.com/default.aspx

I liked the idea, but I think at the end of the day, the up-front costs and the costs of "feeding" the Fueler actually cost more that what you could just drive to the pump.

Also, I don't think this thing would like Iowa Winters all that much.