MarketPress + Pro Site, limit/restrict Product Catalog Only?

I have MarketPress and Pro Sites setup on a site I am developing and am trying to see if we can charge extra (separate Pro Level) to allow the users to turn the "Product Listings Only" option from Off to On within MarketPress.

We deal with retail outlets, so we could sell in-store sites (iPad presentations), or charge more for online, e-commerce-enabled sites.