Calling outside subs and modules in Template Toolkit without Plugins?

You can also pass functions (ie. subroutines) to template like this:

use strict;
use warnings;
use List::Util ();
use Template;

my $tt = Template->new({
    INCLUDE_PATH  => '.',
});

$tt->process( 'not_plugin.tt', { 
    divider    => sub { '='  x  $_[0]         },
    capitalize => sub { ucfirst $_[0]         },
    sum        => sub { List::Util::sum( @_ ) },
});

not_plugin.tt

[% divider( 40 ) %]
Hello my name is [% capitalize( 'barry' ) %], how are u today?
The ultimate answer to life is [% sum( 10, 30, 2 ) %]
[% divider( 40 ) %]

will produce this:

========================================
Hello my name is Barry, how are u today?
The ultimate answer to life is 42
========================================

Have you tried useing the module in a [% PERL %] block?

Now, I personally would write a plugin which relays, say, a MyOrg::Plugin::Util->prettify_date to Util::prettify_date after getting rid of the first argument. You can automate the creation of these methods as well:

my @to_proxy = qw( prettify_date );

sub new {
    my $class = shift;

    {
        no strict 'refs';
        for my $sub ( @to_proxy) {
            *{"${class}::${sub}"} = sub {
                my $self = shift;
                return "My::Util::$sub"->( @_ );
            }
        }
    }
    bless {} => $class;
}