I have worked out how to trigger envelopes (assuming you don’t want to wait more than 4 seconds into the note for it to trigger). Set that Envelope’s delay to maximum (I.e. 4 seconds), and map your triggering variable to modulate that back down to zero. Then draw a Mod Remap curve that’s basically a flat line at zero to the threshold, and max afterwards. The Envelope will be in a wait state until the threshold is hit, then will start.
You can also do this with LFOs, and I think it works better as you can get them to reset back to the waitstate by syncing to tempo.
The Mod Remap curves are awesome and in combination with using the Macros as registers, you can get some Boolean logic going.