Gentoo: USE Flags applications dependencies..
 

For Gentoo:

I appologize if this has been covered, I have tried a few searches with no luck.

I've installed a few major apps from source for various reasons. One of these are MySQL. In order to stop mysql from being compiled each time I emerge a package requiring it, I now have to have a USE flag of -mysql so it won't try to install it. However, I think that at the same time I'm screwing myself over with that USE flag and the applications are being compiled without mysql support.

Ok, so now onto the question:
How can I force the system to recognize applications that I don't emerge, but are installed from other means? And how can I point the system to the install directory the application lives in?

Thank you.

Cool