Control Insert on Group Channel via Midi track


I’m trying to add a GroupChannel, to put LoopMash FX on and run several audiotracks through the LoopMash FX.
But when I put the LoopMash on the GroupChannel, I can’t route a MIDI track to it. If it’s on a regular Audio track; if I put
the LoopMash FX directly on the individual Audio channels, there’s no problem assigning a MIDI track to control it.
I want to control it with the piano roll, ofcourse…

Why can’t this be done, and what other solutions do I have? I don’t want to use an FX channel, because I have no intention of running the dry audio through at all, only wet.