There is http://search.cpan.org/~sburke/RTF-Writer/lib/RTF/Cookbook.pod which is useful in this context. I compiled a small example, which creates a file super.rtf that has superscripts with commata.

use strict;
use warnings;
use RTF::Writer;

my %authors = (
    "Isheng J. Tsai"       => "1,2",
    "Magdalena Zarowiecki" => "1",
    "Nick Riddiford"       => "14,15",
    );

my $rtf = RTF::Writer->new_to_file( "super.rtf" );
$rtf->prolog( title => "Authors" );
$rtf->paragraph( \'', "The authors:" );
for my $a (sort keys %authors) {
    $rtf->print( \'\plain', "$a" );
    $rtf->print( \'\super', $authors{$a} );
    $rtf->print( \'\plain', "," );
}
$rtf->close;
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