Ah, I see, sorry for the misunderstanding. You are right. If the antenna has an inline booster then this is not the solution. For some reason I was thinking that the booster was powered by the antenna/remote 12V signal line from the factory, but of course it is not this way. /Slaps self.
There are circuits like you say that block the DC power from reaching the receiver. My experience is more with active GPS antennas and they can use a little block which has 3 connectors. One to the antenna, one to the receiver, and one to the DC power source for the antenna. This is all pretty much useless to you though, as I dont have a link to a device that would work in your particular situation.
You could probably find a schematic that would use capacitors to block the DC from reaching the tuner, but I dont know how much it would change your signal. I would have thought there would be an aftermarket solution if there were so many cars that used this.