I just skimmed thru the docs and found two possible approaches:

• Template Variables

  my $tt = Template->new({
      VARIABLES => {
          version => 3.14,
          release => 'Sahara',
      },  
  });
  
  my $vars = {
      serial_no => 271828,
  };
  
  $tt->process('myfile', $vars);
  [download]

• Compile Time Constant Folding

  my $tt = Template->new({
      CONSTANTS => {
          version => 3.14,
          release => 'skyrocket',
          col     => {
              back => '#ffffff',
              fore => '#000000',
          },
          myobj => My::Object->new(),
          mysub => sub { ... },
          joint => ', ',
      },
  });
  [download]

Hence you could write a sub current_constants() which is introspecting your current package and return a list of pairs which maps each constant to it's name. Another way could be to check the exporter settings of the defining package.

my $tt = Template->new({
    CONSTANTS => { current_constants() },
});
[download]

Once this works you should also be able to write a TT plugin to do this automatically.

Question That's what you want?

update

°) this was written before the OP added his "EDIT" section.