I have a multi-network configured to allow free blogs

I have a multi-network configured to allow free blogs on sign up. The main site is customized with a dark theme so the adsense code I'm using reflects that. The templates I'm using on the sub-sites all have white or light themes so my adsense code needs to reflect that which means I'll need to create different ad units.
I see where although I have the ability to active Simple Ads at the site level there's no way to manage it. So I'm left with having to configure it from a network level. This causes all subsites to use the same dark ad units. I want the ability to use different ad units all the while giving owners the ability to select to remove these units. Is this possible using Prosites? If so how.
Any responses appreciated.