How can I link the logo in the header of my theme to my parent site

I am using a multi-site setup for a website that is very large. I am using the same theme for a parent site and a number of sub sites for multiple bloggers and sub-sections. I have successfully customized the magazine theme at the network level so that all of the sub-sites are automatically consistent and I really like the look of it but I'm going to need some control over navigation menus. I would like to create a link in my menu that goes back to the parent site from the sub-sites. It seems that it will be very difficult to customize the menu in the magazine theme so I'm wondering if I could use the header logo to link back to the parent site instead. Is that possible? If not would there be another way to include an outside url link at the top of the page so that I can easily take them back to the main site home page? Or would there be another theme that would be more suitable for a community info site that includes community calendars, forums, blogs, and feature pages for artists, musicians, and community orgs. I'm also planning on including a social networking site later on down the road and would prefer them all to use the same theme for consistency.