[HALtheWise]

Assuming the USPS and physical addresses are in the same town, the following format can work quite well:

314 Something Rd / PO 404

Town, City 12345

This works because the postal service tries to deliver to the last thing on the label that they recognize. Using slash as a separator works better than a comma or newline because it's less likely the service you're shipping from will "notice" that you put a PO box in and force the package to send via USPS.