I don't think any car maker would offer a radar detector or mount for one. Guessing the lawyers would say NO pretty loudly....
Would this spare parts kit work to "make" a mount that also uses the goPro camera mount on the windshield? [ame="http://www.amazon.com/GoPro-Grab-Mounts-HERO-Cameras/dp/B003U6Y1OC/ref=sr_1_1?s=electronics&ie=UTF8&qid=1333047777&sr=1-1"]Amazon.com: GoPro Grab Bag of Mounts for HERO Cameras: Camera & Photo@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41qLLBlEcaL.@@AMEPARAM@@41qLLBlEcaL[/ame] Granted, you can only use one device at a time. Or buy to goPro mounts.
I just got that bag of Go-pro mounts for another purpose. You could use the adhesive disks to adhere a mount to the inside of the windshield. Then choose a bracket (probably the J bracket) to attach to that mount. The problem is going to be going from that wierd go-pro bracket to something that the radar detector can mount to. One company had an adaptor to go to a camera 1/4" threaded tripod mount... perhaps if you strip that screw out and attach to the flat base...
Sure... if you have $1,600 and some good skill at concealing the bits in your front and rear bumper: PASSPORT 9500ci - Escort Inc. You can see that it has a 2-LED alert system as what is visible inside the car (plust the controls hidden somewhere out of sight). You might have to worry about radar detector detectors (yes, there are such things) and someone who can spot the bits hiding in your bumper (I've noticed 'em on a few high-end cars now that I know what I'm looking for)
I think there are some, "active", detectors out there too. There is an Audi that I see regularly on the highway on my way to work, that whenever I am near it, it freaks out my V1, all the leds flash, and it screams all the sounds! Crazy?