Gerry,
If I understood correctly he wants to change the template on a per user basis (stored in the session) so modifying the config files is out of scope.
If this is the case, you should be able to easily modify the multitemplate template [1] to decide the template based on the user logged in instead of the namespace. And then just write a plugin to configure it if you wish.
The big con is that you lose style.ini support, but that shouldn't stop you from using it.
The big pro though is that something very similary is already written and working, so by all means please build upon it instead of reinventing the wheel.
[1] http://tatewake.com/wiki/projects:multitemplate_for_dokuwiki
-- --Terence J. Grant(tjgrant@xxxxxxxxxxxx) -- DokuWiki mailing list - more info at http://wiki.splitbrain.org/wiki:mailinglist