Activate Premium themes with Authorize.net gateway

Supporter plugin offers Premium themes, but has no Authorize.net merchant gateway. On the other hand Membership plugin has the Authorize, but cannot offer themes for Members.

My goal is simple:
1. users can register for free and make blogs with free themes
2. users can pay monthly via Authorize.net for premium themes (PayPal can be just an additional option).

What is the best way to achieve the above goal?

Thanks