How to give a pro site a specific template?

If i want to set up a few themes for pro-sites and allow pro site users to select them on sign up what do i do?

i am using a plugin that allows people to pick themes on sign up that are completely set up and it works fine for themes that are free.

they then upgrade for the additional themes and when they select a theme from the appearance > themes those are not set up.

i thought about giving all themes away for free but charging to blog allowing all blog templates to show on the sign up page.

I also thought about giving the first X days away for free so if they select a pro site theme on sign up it would be complete but then the issue is if they DO NOT PAY for the upgrade im assuming they would get a white screen and i would have to go in and change their theme manually.

ideally the process would go like this.

user signs up for free site and they get a template with new blog templates
they play around a bit and i upsell them a pro site theme

they upgrade to become a pro site

and then they can choose what ever theme they want and it is already set up. ??