Multisite configuration subdomain.domain.com/site

I am trying to figure out what is the best way to support a multisite configuration as follows. I have a need to support any subdomain I want along with any site name I want. For example I want to allow for the following.

subdomain1.domain.com/site1
subdomain1.domain.com/site2
subdomain2.domain.com/site123
subdomain431.domain.com/sitexyz

I am hoping that the Multi Domain plugin would allow me to pre-configure any subdomain I wish, and then allow the user to select whatever site name they wish.

I'm not afraid of a little custom coding if the right hooks are around to be leveraged, plus, I'm already custom coding my wp-signup.php page also, so hoping the Multi Domain plugin could be tweaked easily to support what I am looking for.

Thanks in advance.
Shawn