Do you support multi-box shipment?

It would be a great feature to be able to build a shipment with multiple boxes going to one address. I know that FedEx, UPS and DHL allow you to create a master tracking number that ties all included boxes with different tracking numbers back to one number. This allows packages that cannot fit in one box to be shipped, travel and deliver together. USPS does not allow multi-box shipping under one tracking number.