Just load this form's page with $mech->get(...) and do: 
$mech->submit_form(
    form_number => 1,
    fields => {
        target => "Affiliate",
    },
);

[download]
But you need to check form_number param by yourself.

In reply to Re: Using Mechanize With Odd Query String by Gangabass
in thread Using Mechanize With Odd Query String by varanasi

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