Yeah, sometimes you want to do dynamic includes with HTML::Template. It's come up on the list before.

The first thread returned from the above link suggests using two H::T objects (source):

my $t = HTML::Template->new( "foo.html" );
my $i = HTML::Template->new( "inner.html" );

$t->param( INNER => $i->output( ) );
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That way, having a TMPL_VAR called INNER in your main template will allow you to dynamically stuff the contents of another template inside.

It's a bit backwards, but I've used this method before...

Update: Instead, you may wish to write a filter (source)