I've always had a PO Box for my address. Back when it didnt matter, it was fine for your license, but these days it wont fly. I'm really surprised your state still accepts it for the DL itself.
What you do is this, and I got it right from my Postmaster when I asked the question for my license a number of years ago, and this is what I've been doing since.
Your address looks like this:
Jimmy Gunbuyer
RR4 Box 320
PO Box 3006
Winchester, VA
The first line is the physical address, the second, where the mail will be delivered. According to the feds and state, its a legal address.
The funny part is, the last three "physical" address's on my license, were not in the same town as my PO Box, but that doesnt seem to matter, you just have to have a physical address. In reality it doesnt, as you have to have all the ID to get a box these days anyway.
The whole thing is a joke anyway. Around here, we dont have 911, so the address's are still a RR number. If you put that in a search like Map Quest, you get the center of the zip code for the location. The fire companys address is a little plaque on your house with a zone and number for their use, so that isnt even an "address".
They are getting things tightened up, but its still pretty much in flux out in the boonies.