I have read a few people installed the loaded mirrors on to their Express, then had the dealer flash the pcm and everything worked. Here is a responce from Ram Tech in the ask a tech forum. I think the dealer needs to upload the option codes for the mirrors to work.
Brad12kx was kind enough to pass along his VIN and here's what I came up with - it appears that all the door modules are the same with regard to capability, so those shouldn't be an issue. The two option codes I found are LEBP for the supplemental signals and LECP of the puddle lamps. If the system will allow the dealer to program in these option codes, the tech should be able to reconfigure the truck and they should work. If the system won't allow them to add in these options, ask them to file a STAR case and see if they can help.