infoforme on "Multisite into sub directory?"

Hi

I run a few websites where I have my domain.com and a few sub domains.

I know multisite will all me to run on entire sub domains so:

mydomain.com > sub1.mydomain.com sub2.mydomain.com

But is there any way I can run multisite from sub directories, like:

mydomain.com/blog > sub1.mydomain.com/blog sub2.mydomain.com/blog

Any pointers would be great.

Many thanks

Jim