Domain mapping – with custom subdir

Hi, domain mapping works great, but I want to add a directory to the end of the path. Example:

Main wordpress install on: example.com

Networked blog on: blog1.example.com

Domain mapped to: blog1.com

And now we want to have a custom subdir: blog1.com/shop/ with some files that will lead to some separate html files.

First I thought that it was as easy as adding a dir/files to the blogs.dir/2/ directory but it appears it isn’t. Any ideas/suggestions?