in reply to Template toolkit INCLUDE_PATH question
Interesting question! I can't answer it, but this reply might help point you in the right direction.
Template::Provider's paths method will return what you want, but I don't know how to retrieve the appropriate provider object(s) from a Template object.
$template->service returns the Template::Service object; $template->service->context returns the Temmplate::Context object. I can't figure out how to get the providers, though.
You might get a more helpful response from asking the TT mailing list.