@JM8UTW I looked into this a while ago. Simply rent a PO Box. You can do that online. From what i heard you will never recive any letters by the FCC because they send everything via E-Mail only. So for how long you keep renting that PO Box is _theoreticaly_ up to you. But you have at least a physical address for getting the licence in the first place.
@DL9DX Thanks! I've decided to get a U.S. address via P.O. Box to obtain the FRN. If all FCC communication is email, I'll decide how long to rent the P.O. Box, as you suggested.