I have a branch in the Deliverance SVN which makes the theme URI, the rule URI,
and the serializer
component all overridable by setting keys in the WSGI environ (via API functions
I have added):

  http://codespeak.net/svn/z3/deliverance/branches/urienv/

I expect to get Ian to merge that branch to the trunk before he releases
Deliverance 0.2.  Please
check it out and see if it would work for you (you will need to write a bit of
"ingress" middleware
which uses the API to override the theme URI).