assigning cc's to the knobs (on the rm1x)

[Switch Flipper]

It seems that I can't assign cc's of my choice to the assignable knobs -- is this correct?  All I can assign to the knobs, as far as I can tell, is CC 94,93,91,10, and 7.  I want to assign CC 72 to one of the knobs.  Is this impossible?   thanks