The last time I had a PO box, it wasn't from the post office, it was from a company called mailboxes USA, they privided me with a Suite# - Which makes people think that you are sending mail to an office. The clerk suggested the suite # because she said that people often come in looking for an office, not realizing that it is a mailing service. Also they accept and sign all paper work from all companies. Keep in mind though, it has been quite some time since I've done this.
Thought this might be of some interest. If you're serious about going this route, PM me for other suggestions.

Doc