Although Appath can allow you to hide the postage paid on your USPS labels (please read this article for more info on how to print a label without showing postage), if Carrier Insurance is added to a USPS shipment, the postage paid must be displayed on the label regardless of the carrier (Express 1 or Stamps.com).
You can always use Shipsurance instead of Carrier Insurance, if you wish to hide the postage fees.
Additionally, Express 1 has NSA (Negotiated Service Agreement) rates, so they are forbidden to display their rates on the labels. However, this rule is overriden by the USPS requirement to have the postage shown on all labels that have carrier insurance added to them. As well as, some countries (like Brazil) that require postage to be displayed.