Manually change New Blog Templates after sign up?

Hi guys,

I'm trying assign a different blog template to a Pro Sites 'Pro Account' signup. Since this is (not yet) possible throught Pro Sites automaticly I was wondering if it is possible to add a function to New Blog Templates instead, allowing for a manual change when a customer upgrades to pro. This would be a fantastic temporally option (I think) for a lot of people. (For example: https://premium.wpmudev.org/forums/topic/pro-sites-and-new-blog-templates-1#post-168356)

Anyway I have no idea if it's an easy fix I'm just trying to work around this...

Thanks,

Nick