How do I disable access to certain plugins on certain sites on my network?

Hi, thanks for taking a sec.
I'm building a brand new mu site.
The main site will be a directory theme(not mudev.)
I will install the problogs plugin to allow visitors to have their own blogs on the site.
I will have many plugins on the main directory theme/url, but I will want to restrict blog owners from access to many/most of the plugins. What is the best way to achieve this?
Thanks for your help & patience,
Yohan