TT's process method will happily work with data from a scalar, you just have to pass a reference to the template text (so that it knows it's not a file name).

use Template;
my $tt = Template->new( );
my $data = { foo => 'bar' };
$tt->process( \qq{[% foo %]\n[% FOR i IN ['A'..'Z'] %][% i %]\n[% END 
+%]}, $data, \*STDOUT );
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I do this all the time putting the template source after the __END__ marker and then slurping it into a scalar from DATA. Or you could get fancy and use Inline::Files.