It’s possible to trigger envelope / lfo with midi, sending an Envelope Threshold CC16, with a 0 value, and a 127 value before.
I set an middle envelope mode (AR / AD).
A specific CC and / or any Note > trigger option would better, but it works.
I think it’s possible switching Envelope Mode too, but it doesn’t seem practical.
Actually, it doesn’t work properly.
Change trigger mode (AD, AR, FLW) can work too but I experienced some delay.
The best I experimented is CV control by A4…
Analog Heat : Drum synthesis and sequencing
…following @qlamerand advice.
“Hybrid synth“ using AH and Keystep
Told you i couldn t get it to work right 
It is possible to trigger with midi, but there is latency, and you can’t trigger very often.
With an offset and trigging every half bar it should be doable.
I suppose if it was working right Elektron would have implemented a midi message.
A midi to CV thing should work, as it works with A4’s CV.
I also tried audio signal in the CV input. It worked, but I don’t remember what was unsatisfying apart from using OT CUE OUT only for that!
Solutions for sure!