2016 Promaster City Rear Speakers

I have a customer with a 2016 Promaster City STL with the UConnect radio containing only balance and no fade. It also has the VW style locking harness (71-6523) on the back of the radio. They purchased the vehicle with front door speakers and tweeters in the A-pilar. They want to add rear speakers in the factory location which seem to be 4" mounting plates. There are no pre-wired pigtials in the rear factory location. Also, there are no wires pinned for the rear channels at the radio. I tested the rear speaker out pins at the radio with a DMM on VAC and hooked up a test speaker to the pins....nothing. I've looked at a couple forumns reguarding this issues and they said the dealer has to turn the rear channels on with their scan tool then the factory harness has to be pinned for rear speakers. So I called our local dealer and they were pretty much clueless as expected. After hours of research on their end, they told me Chrysler would have to write a firmware, then they would have to download it, then they would have to upload it to the vehicle. Sounds like a bunch of ignorant B.S. to me. Also, I tried going into engineering mode on the radio and turning the rear speaker output on. You hold radio, meadia, and browse/tune for 5 seconds then go to audio engineering to change a setting. That setting was not on the radio. I know I can add a aftermarket amp with a LOC or a aftermarket radio to accomplish what they wanna do, but the customer wants to keep everything factory. Has anyone ran into this problem or is my only option aftermarket?I drink current, eat ohms, and bleed voltage

All manufactures are doing this now! They have locked the functions in the vehicle so you can't upgrade a base model with premium options with junkyard or salvage parts. This is the case for radios, power mirrors, heated seats and any other options that were available upgrades from the stripped down base. Even if the wiring and relays are there they wont work until you pay the manufacture to update your vehicle option codes in their system, and then pay the dealer to re-flash your vehicle. Their reasoning was to cut down on vehicle theft and the sale of stolen car parts. Even the radio is locked to each vehicle by vin#. But in the end they will get theirs if you want factory upgrades or you will have to buy it with them already new. So unless you want to play the Dodge and dealer up grade game. You'll have to do aftermarket head unit to get the rear speaker function. I don't know how much Dodge charges but it wont be cheap. Someone on another forum did this with a factory remote start that he bought outright and installed himself and it wouldn't work. So he took it too the dealer and they told him that he had to pay GM $120 to update the option code and the dealer like $74 to do the reflash. Then it worked fine.