I'm not aware that it would be possible to simply turn off the controls (but might just not know the desk well enough).
What you could do to achieve the same effect, is to "disconnect" the Console cable (DB25) between the Console and the Rack. For example, by putting a DB25 serial switch between them.
I use a switch like that to switch the desk from Mixer operation to ProBox operation (i.e. like a 24 Channel Mackie Control unit).
The ProBox sends different messages to the display, and things can look a little messy on the display when switching back to Mixer mode. But if you'd have nothing connected on position B of the switch, the D8B's connection to its computer (aka rack unit) would be interrupted, and brought back with no changes, when putting the switch back in the "A" position.
Maybe this is not exactly the type of solution you were looking for, but as a workaround, it would work
I have no good ideas how to prevent wet hairballs from dripping into the faders, though, short of always putting something over it