I was told all of those same things. My selling dealer said he talked with Harley and they said it could not be done. It didn't make sense to me since I already had TPMS on the bike.
Here is what got my attention. One day I was in the garage with the trike and when I started it, I didn't get a warning light. When I pulled out of the garage, I got the warning light. So what was happening was - the rear tire that was taken off was in the garage and the bike read it. That made me thing, it could be done.
See the below thread and you will find a bit more. Another guy here PFwiz had a Road Glide and he had it done too.
True about the Harley TPMS - the holes in the new wheels are larger - so, if I recall, they simply mounted the sensors inside. They did not need the stems since you are only using the sensor, not the valve stems.
One last thing, after I had mine done, someone mentioned that there was a kit that could convert the Harley TPMS to the regular size. If you can find that thread, it may be helpful to you.
Good luck.
TPMS and Harley (triketalk.com)