how to define template_root in controller?

I have implemented this with a patched version of the theme_support
plugin by Matt McCray. There is a patch floating around that makes it
compatible with Rails 1.2 (the official version is only compatible
with 1.1). I have submitted some patches to Matt, but he seems to be
AWOL.

Rails 2.0 will support the notion of view paths which will make the
whole process work a lot smoother (http://weblog.rubyonrails.org/
2007/2/4/new-feature-for-rails-2-0-multiple-controller-view-paths).

I'm currently in the process of deploying a major site using this
feature and I've got a writeup in the works about how I set it all
up. Should be posted in the next week some time in my blog at
http://darwinweb.net/. I might even fork theme_support and release a
plugin focused around multiple domain applications.