render_to_string inside method shared across several controllers

I use render_to_string to generate short reports (in HTML) under
certain conditions when users access my application. The reports are
stored in the database and uses database information at the time they
are generated (and can thus not be generated later, e.g; when you want
to consult them). The reports are generated the same way regardless of
which controller has been accessed. Conditions for generating reports
are tested in a before_filter and the method that generates the
reports and that calls render_to_string is in a helper. The
render_to_string uses both a layout and a view template.

My problem: there is (as far as I can se) no way to specificy where
the view template is stored. Instead, render_to_string assumes that it
is stored in app/views/<the_controller>, where <the_controller> is the
controller accessed. But I need this to work for several controllers!
The only solution I have found is to store copies of the view template
in all the app/views/<controller> directories. Highly inelegant, and
will lead to maintenance nightmares. Any suggestions? (Maybe I should
put it all into the layout and just have empty view templates?)