That's interesting that dealers won't do this... wonder why. Not something I would attempt myself.
Yeah, even though the dealers are charging something like $130/hr for labor. It's just a real hassle routing the wiring, so cars at the factory are designated from the gitgo to get certain options so they are wired while the chassis is bare. The dealers are too lazy/dumb to do the installs.
I had backup sensors installed before I picked up the car, but it was done by a third party the dealer dealth with. The dealer wouldn't do the OEM motion detector.
In fact, the dealer wouldn't even remove my rear view mirror - not even for $130/hr labor. They were as afraid as everybody else was about cracking the front windshield. Yet the Helm shop manual via CD has a video on how to do it. Seems it requires a $400 tool which you would think the dealer had. It's a modified Vise-grip. Just clamp it on and tap gently upwards.
Unless you are willing to custom order your car and wait 6 months for it, most have to settle for whatever's on the lot.