It looks like you could update WA_eCart_UPS_PHP.php
and update the code adding a line before:
$UPS_XML .= "</Shipment></RatingServiceSelectionRequest>";
and make it:
$UPS_XML .= "<RateInformation><NegotiatedRatesIndicator/></RateInformation>";
$UPS_XML .= "</Shipment></RatingServiceSelectionRequest>";