Any way to make Pro Sites ignore certain "Core" subsites?

Hello.

We have Pro Sites running with great early success on our network. There is one issue however.

Our network has a core group of sites (around 10) that are considered "Core" sites which have MUCH higher upload quotas and contain NO theme/plugin restrictions. We don't want these sites to be in any way constrained by the Pro Sites plugin.

It does not appear to me that there is a way for us to set them up so that Pro Sites 'ignores' applying its Level restrictions to them. Am I overlooking something?

These ~10 sites need to have free reign to be used without restriction, while we continue to use the Pro Sites plugin and its Levels for new blogs created by our network's user base.

An example of a problem this is causing is this:
We currently use the advertising addon to append a network wide ad to the end of FREE account blog posts. Because our "Core" sites are technically FREE accounts (not Pro Sites accounts), they are getting the ad code in all of their posts, which we do not want.

However, we also cannot simply create a high permission Pro Sites Level to apply to these Core Sites, because then that Level would be visible to users going through the Upgrade process, right?

I hope this made sense. I would greatly appreciate any tips or advice on how to address this issue.