Disable or remove main site from 'my sites' list

I have created a membership site with pro-sites on a mu wordpress install. My main site has monthly membership options, where user can subscribe and create new sites of their own in the network (typical wordpress.com site).

When users login to their dashboard, what they see in 'My sites' list is all their created sites (as admin), but in addition they see the main site (as subscriber).

I need to remove this main site entry from this list. How can I do this.

All main site management will be done directly on the main site via my custom pages. I do not want wordpress mu to list the main site dashboard.

Another question to this is that, pretty plugins works all well for user created sites, but for main site it shifts to wp dashboard - I do not want this. How to prevent it?