Hide Account Number Fedex WSDL

Anyone have an idea on how to hide the account number in the FedEx API/WSDL?

 I have tried the following among a thousand other combos:1 request.RequestedShipment.LabelSpecification.CustomerSpecifiedDetail.MaskedData = new LabelMaskableDataType[1] { LabelMaskableDataType.SHIPPER_ACCOUNT_NUMBER };
2
3 //and
4
5 request.RequestedShipment.LabelSpecification.CustomerSpecifiedDetail.MaskedData = LabelMaskableDataType.SHIPPER_ACCOUNT_NUMBER;

 

But nothing seems to work...  If anyone has any idea on how to mask the account number from the shipping label I would appreciate it.
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