I started discussion of this concept in Re: Re: Re: Why CGI::Application. Basically, you have a single function in your CGI::Application baseclass which does all your output. The function accepts a template name, an output type, and parameters. Something like:

my %types = (
    pdf => {
        extension => '.pdf.xml',
        module => 'PDF::Template',
    },
    xls => {
        extension => '.xls.xml',
        module => 'Excel::Template',
    },
    html => {
        extension => '.tmpl',
        module => 'HTML::Template',
    },
);

sub print
{
    my $self = shift;
    my ($tmpl_name, $type, @parms) = @_;

    my $module = $types{$type}{module};
    my $template = $module->new(
        filename => $tmpl_name . '.' . $types{$type}{extension};
    );

    $template->param( @parms );

    return $template->output;
}
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That's the basic skeleton. Obviously, you'll want to extend that a bit, add some error-handling and defaults. But, Excel::Template and PDF::Template support the exact same API as HTML::Template, by design.