Rails IIS and virtual directories

Hi,

I've followed all the instructions for setting up Rails with IIS and
FCGI. Everything works fine when the root of the web site is set to the
Rails app public directory.

I would like to be able to set it up using virtual directories, but
when I've tried to do that, all of the generated links map to
/something rather than /mydir/something.

Is there a way to configure either IIS, ISAPI_Rewrite or Rails to
correct this?

TIA,

Ant