Offering New Blog Templates according to ProSites level

I've found a lot of questions on this going back a few years but no answers so far, so apologies if it's been covered and I missed it.

I'm trying to offer a range of plug-and-play websites, with an expanding set of plugins and themes for each higher ProSites level.

I've just spent a couple of weeks setting it up and making a couple of templates for each level, using the extra plugins and premium themes, but there doesn't seem to be any way of restricting the 'premium' templates to paid users.

In fact, a free user can sign up and select the top level template, and all premium plugins are activated on the resulting site.

I missed the new features discussion on NBT, so I was wondering if anyone had come up with some sort of solution for this?

I had thought the pro level plugins and themes would simply not be available to a free user, but that's not the case. Anyone know a way to control this?

Or an easy way for users to select and install a template AFTER they've selected a pro sites package?

About the only other option I can think of is walking pro users through an import process, but that defeats the purpose a bit?

Any suggestions much appreciated!