Thanks, everyone. Yes, actually, I do own the Passport 8500 and I agree that it's a great detector. And, I've looked at the "clip-over-the rearview" option, but I just don't care for it (thanks, anyway!).
What I was really hoping to find was an option (as I've said, I've seen it) where the detector is installed as an integral part of the existing rearview mirror. That way, it's mounted as high in the car as practical and is invisible to others. It also had some nice features, similar to the Passport. But, I've not been able to track it down!
If I come across it, I'll post a message.