Hi there - I've been testing the User Registration Add-On tonight and, in doing so, have been reading a number of the discussion threads, including the questions bghouse raised in this one: http://forum.gravityhelp.com/topic/user-registration-add-on-questions
bghouse, in case it helps, I think there's a single form solution to the scenario you've raised. I've whipped up a quick screencast to show you what I mean. Hope it helps you and others: http://screenr.com/R3t
P.S. Feel free to ignore the pricing field in the demo form, as I don't think that was part of bghouse's original set of questions.