Hi there,
I’m building an automated Ableton set and seeking to turn the sustain on/off from my DAW. This kind of thing is possible in most VSTs, but for some reason the midi machines parameters are accessible only through midi (and only with anachronistic CC mapping, not with midi learn). Has anyone faced this, found a workaround or similar?
Hello, welcome here 
Yes, Midi Machines are midi effects, nothing else. And unfortunately, they can not be midi learned in MG2.
what i do in this situation is create a new midi track in ableton to route sustain (coming from a pedal) to a synth (on a separate midi track, not in mg2).
yet another midi track is used to route note info from mg2 to that synth.
this technique also works with external pitchbend / channel pressure / aftertouch.
how do you want to trigger sustain on? via pedal or ableton clip? or?