Funny, I've been thinking of starting this exact same post. I also want a rider backrest for my 03 FLHTPI with the air ride seat. I love my air ride seat, and I've heard too many good things about rider backrests. I went to the dealer recently inquiring about this, and the parts guy took the reciever mounting bracket out of a new (basic HD) backrest package. We walked it over to a Police bike with the air ride seat, and we held it next to the mounting bolts. It looks like it should work. But....the reciever bracket would be visible (and would not look good) and I want the Mustang Passenger seat, which sits on the same bolts that the reciever bracket would mount to.
I've been thinking about going to a machine/welding shop and checking on having a bracket fabricated that would attach to the metal frame on the bottom of the seat and wrap around up behind the seat. I don't know if something could be fabricated that would allow the use of an adjustable backrest, or if it would be set in a permanent position. I've heard that the Mustang rider backrests are the way to go, better than the HD's. Having a backrest attached this way seems to me to be the best choice, as the backrest would move up and down with the seat (and the rider).
Also, just last night, I looked at the Protac website (www.protac.net). They make rider backrests, and the one they have listed/pictured for a Road King looks like it might work. It appears to attach to the fender rail from each side. I don't like the look and shape of the Protac pad, though. Maybe an oval pad could be rigged to attach to that bracket.
As good as the air ride seat is, someone out there must have a rider backrest in use on/with this seat. Hopefully, someone else will chime in, and we will figure this thing out.
The civilian H-D backrest and bracket will work. You have to mount the bracket backwards of the way the civilian one is mounted for seat clearance and YES it will be exposed to the eye. The goldish color of the mounting bracket finish is not very pleasing to the eye, nor is its mechanical appearance with all the adjusting holes. But for comfort there are alot of police that use them and don't care how they look.