Making user blogs look like my main page?

FigthNomads.com is my site. I am using the LIfestyle theme from StudioPress. What I want to do is make it so when someone views my user blog it looks as if they never left my site. Ill try to give a better example.

Say FightPassport.com was my main website. When you click on a user blog I would like the user blog to look like this page: http://fightpassport.com/2008/06/

So the user blogs have the same header, same sidebar, etc. It looks as if the user blog is still part of the main site, not a seperate blog.

What do you suggest is the best way to do this? Should I have one of the themes from the 100 theme pack modified to look like my main theme? Or should I have a custom theme created?

I hope this makes sense. Thanks for the help!