Hiding MarketPress behind the Members plugin

One of my clients really likes what we've done with MarketPress and wants to know if she can hide an eCommerce solution behind a Members / Registered users solution.

I have already sold the Membership plugin to a client this week but had no real time with it (yet). I need to draw up a quote for my eCommerce client and need to know if the Membership plugin would work in this scenario - or is there another, more elegant method of hiding MarketPress to only registered users?

Thanks in advance

(Too much work, someone give me more hours in the day!)