Hi Jason,
Firstly, I am not affiliated in any manner whatsoever with the InstantPay plugin.
Here's what I hope to accomplish. Please bear in mind I have zero coder experience. In the net result I'd like to see this plugin - http://www.wp-instantpay.com/wp-instantpay-help-index/ - fully/seamlessly integrated with s2Pro. I know you've got extensive PayPal API/IPN capabilities built in, so would the following scenario be doable:
1) Affiliate sends visitor through their affiliate link and visitor's browser is cookie'd via InstantPay.
2) Visitor signs up as Level0 (free) s2Member.
3) They eventually upgrade to paid(Levcel1) member.
4)InstantPay pays affiliate, site owner and equity partner in real time at point of upgrade.
5)s2Member fully takes over after that and automatically processes upgraded member as it normally would.
The beauty of this from your point of view, Jason, is that you'd have a 3rd option available in the API / Tracking section that would pay you real-time commissions on any sale generated from people purchasing the plugin through your aff. link.
Thank you for your consideration.
Best regards,
Mark