I had some trouble updating the return url values when the Submit button was clicked. So my solution was to update the return urls when the triggering field was changed. Then when the submit button was pressed the return urls would already be set:
var $jQ = jQuery.noConflict();
$jQ(document).ready(function(){
var campField = $jQ("#Campus_Preference__c");
var URL = 'http://www.defaultpage.edu';
$jQ(campField).change(function() {
var value = this.value;
switch(value)
{
case "Seattle":
URL = 'http://www.seattlepage.edu';
break;
case "Charlotte":
URL = 'http://www.charlottepage.edu';
break;
default:
URL = 'http://www.defaultpage.edu';
}
$jQ('input[name=returnURL]').val(URL);
$jQ('input[name=retURL]').val(URL);
}).change();
});