Thats not quite correct:
The removable knuckle has nothing to do with the shifter its only used when a MMX compatible Avid brake isnt used in conjunction with remote.
The shifter mounts onto a small extension plate that comes with the MMX remote.
If your running this style of X9 Shifter then it will mount directly onto the remote using one of the two threaded holes that the original clamp attaches too:
If your running this style then you cant and you can mount the shifter as per normal alongside the reverb remote.
This image should clear everything up.
You use the little knuckle if your not using an MMX avid brake (it effectively replaces the darker grey brake section of the clamp).
The shifter extension can also be removed if your X9 shifter isnt compatible, it simply unscrews from a removable back plate insider the reverb remote.
Also worth noting that if you do run the remote upside down on the opposite side you will not be able to direct mount the shifter to it (but you could still direct mount an MMX Avid brake).