I noticed on PayPal's Subscription Button (see attachment), you can select to create a "Trial Period". That trial period doesn't have to be FREE! In other words, you can charge a larger initial one-time setup fee.
Does PayPal let you set this up in the API used to create the subscription payments in ProSites? If so, this wouldn't be that difficult to implement.
The other option might be to have MarketPress handle the initial payment, and it then triggers ProSites to handle the recurring payments from there.
What path would be most reliable, and simplest to implement? Suggestions Please!