This topic was recently discussed on the TT mailing list. There were some options given, but they all required passing in a reference to a hash or a sub that were then populated.

An option that would work in your situation, would be to use Template::Alloy and the poorly documented process_simple method, which has more restrictions than the process method - but doesn't create a copy of the passed in variable stash.

Template::Alloy also gives you access to features that will be in TT3 such as regex construction and self modifying operators such as //=.

use Template::Alloy;
use Data::Dumper qw(Dumper);

my %vars;
my $out = "";
my $t   = Template::Alloy->new;

my $data_str = q{
[% foo = "bar" %]
[% bingo.bango.bongo = /matchme/ %]
[% a //= []; a.0.b.3 = "C" %]
};

$t->process_simple(\$data_str, \%vars, \$out) || die $t->error;

print Dumper \%vars;

__END__
prints:

$VAR1 = {
          'a' => [
                   {
                     'b' => {
                              '3' => 'C'
                            }
                   }
                 ],
          'bingo' => {
                       'bango' => {
                                    'bongo' => qr/(?-xism:matchme)/
                                  }
                     },
          'foo' => 'bar'
        };
[download]

Disclaimer - I wrote Template::Alloy so I *may* be a bit biased towards its use.