I'm wondering if you could process a template twice to achieve what you want. For example, on the first pass, HTML::Template will parse this code:

<TMPL_VAR name="include_link">
[download]

by passing  include_link => qq/<TMPL_INCLUDE name="$custom_link">/ to the param() method of your template object. So, considering for example that your $custom_link is set to 'foo_page.html', the initial template should be parsed into this:

<TMPL_INCLUDE name="foo_page.html">
[download]

Then, you simply have to use this parsed output to initialize yet another template object and 'reparse' it the last time to get exactly what you want.

I'll try to build a little sample script for you to look at in the mean time ;-)

UPDATE: here's some sample code implementing what I was just talking about:

main script:

use strict;
use HTML::Template;

my $tmpl = new HTML::Template(
                              filename => 'first.tmpl'
                              );

# generate custom page link...
my $custom_page = "second.tmpl";
# inject a custom piece of Template code
$tmpl->param(special_page_include => qq/<TMPL_INCLUDE name = "$custom_
+page">/);

# process custom built template..
my $tmpl_final = new  HTML::Template(scalarref => \$tmpl->output());
print $tmpl_final->output();
[download]

first.tmpl

Including custom page...

<TMPL_VAR name = "special_page_include">

-----------

rest of the page
[download]

second.tmpl

SECOND PAGE!
[download]

script output (test run):

Including custom page...

SECOND PAGE!



-----------

rest of the page
[download]

"There is no system but GNU, and Linux is one of its kernels." -- Confession of Faith