This is not currently possible and may never be possible...no one has deciphered the new Global B system to the point where we know what's needed to add options like this. On the pre-refresh trucks it's a major project - you need to change both front seats, the HVAC panel, the driver's window controls, four harnesses and three modules in addition to the mirrors. Then you need to find someone who can do the programming - I believe WAMS can do it but i'm not positive. But you're going to be spending at least $2k in addition to the cost of the mirrors themselves.
I decided it's not worth the cost and time after researching the project for my truck. Though I agree that it's ridiculous they aren't included in the LT package in 2019 and on since my 2010 LT had them - along with a multitude of other things my 2021 is missing - like a power passenger seat, auto-dimming rear-view, lighted mirror visors, and sufficient interior lighting.