package My::App;

use base qw(CGI::Application);

sub load_tmpl {
  my $self = shift;

  my $template = $self->SUPER::load_tmpl(@_);
  # add some global params here
  $template->param( ... );
  return $template;
}

sub runmode {
  my $self = shift;
  my $template = $self->load_tmpl('filename.tmpl');
  $template->param( ... );
  return $template->output;
}