thanks @[deleted] and @dubbylabby
I'm actually getting this to work, (still ironing out the bugs though) using the matrix in Imaginado LK. This started out as an iPad controller for Ableton live, but now has a midi mode for use in AUM etc as an AUv3.
You can set up clips in a grid like in Live, and trigger them from a midi controller. Each clip is a piano roll midi sequencer, and they've just added the ability to record CCs
So have a clip that is set to a 1 bar launch quantise. I hit my controller during the bar before I want it to take effect, then as the bar rolls over, it selects a specific loop in GTL, enters record mode, and also exits it after a certain amount of time, in my case 4 bars.
If you can do the scripting of Mozaic, that might be a better option, but I'm a bit hesitant to go there. This is a little fiddly, but it seems to work! You could script an entire song this way I think.
Here's a lil vid. I wasn't playing nothing so nothing was recorded but you can see what's going on.
https://youtu.be/HE2LRpPFpw4
Note the piano roll is not doing anything in this vid. The controller info is drawn in the section below. but you can see the timeline scrolling in the piano roll, and you can see the clip flashing after i trigger it (top left corner), until the bar rolls over.
Note also my very technical paper overlays on the midi controller. I figure I can swap these between songs as some button assignments would vary.