I am creating a multi-site, which will be a collection of bloggers using my custom cms and server. I am telling the participating bloggers that they can give visitors their customized domain names, but that the address line at the top of the page will reflect the true status of the blog as a folder on the larger portal.

Is there a way to mask the true address without running afoul of G and other SEs?

Example, with fictitious names;
Portal page: www.ExamplePortal.com
Typical blog page: www.ExamplePortal.com/Mikesblog

URL for Mike's friends to use (made possible by a 301 redirect, approved by G): www.ExampleMikesblog.com

What Mike wants his friends to see in the address line at the top of his pages: www.ExampleMikesblog.com

Will the SEs hate us for masking the true url in the address line? What are the best links on webmaster world to help me research this?

[edited by: incrediBILL at 12:16 pm (utc) on May 20, 2009]
[edit reason] exemplified to eliminate real fictitious domains [/edit]