If I understand correctly, it sounds like you are doing:

<form method="post" action="/cgi-bin/myScript?location=value">
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and by doing so, you have no access to location parm via:

my $location = param('location');
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If this is the case, I would suggest you use a hidden parameter ala:

<form method="post" action="/cgi-bin/myScript">
<input type="hidden" name="location" value="val">
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you can then access the location value via the param call.

UPDATE: in re-reading, it appears that you are wanting the form var to appear in the browser location field for a POSTed form. If this is the case, then I am not sure there is a solution