iframing out submits isnt really going to work well with multipage submits. The second page the "action" space you want to iframe will be in a different location and most probably a different size.
I've tried playing games with onSubmit and javascript but it never works right in every browser.
For my money godcpa style iframes are a one trick pony. Single page submits work great, everything else is a bagful of fail.
And, to beat a dead horse that everyone always adds to these threads, the traffic you send through a single page submit is going to be about 0% useful to the advertiser. All those hits you get, all those submits, not a single one will go past the first screen. They WILL catch up to you. Spread your traffic out across many networks, many ads, and make sure you not only send junk traffic to get your conversions down, but some targeted PPC at it as well to get QUALITY conversions.
The big problem with godCPA is that it will convert TOO well and won't last. It's easier to get conversions but more work on the back end to keep the traffic looking reasonable.