perhaps Brian Ng's http://search.cpan.org/~brianng/HTML-DynamicTemplate-0.95/DynamicTemplate.pm will be helpful?

"Template variables may be set within the template itself with the special $SET directive. This is useful when setting variables for use by included templates. Example: $SET(PAGE_TITLE, "What's New"). Note: Be sure to escape quotes (") and closing parantheses ()) as HTML entities."

or Sam Tregar's own extensions, notably HTML::Template::Expr? (and there's a listserv, http://lists.sourceforge.net/lists/listinfo/html-template-users)

...the Philip Janert article at http://www.perl.com/pub/a/2007/02/02/htmltemplate-widgets.html appears (IMO, at first glance] to be a tad off target, but I'm still trying to chew on a few of the observations there because of a nagging sense that they apply to your issues. (Oh, disclaimer, again: Aside from the previous disclaimer ("ignorance") one should note that I have been wrong before; perhaps even more than once.)