Yeah, what you want to do is pass some sort of session identifier to each frame. This will probably involve you writing session management capabilities into your script. A la:

print $query->frameset({-cols=>'25%, 75%'},
     frame({-name=>'left', -src=>"./left.pl?id=${identifier}", -method
+=>'POS
+T'}),
     frame({-name=>'right', -src=>"./right2.pl?id=${identifier}", -act
+ion=>"
+./right2.pl", -method=>'POST'})
);
[download]

Then left.pl and right.pl know which session to lookup from your backend storage.

cp
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