printing Envelopes back onto Ableton Midi Clips

Hi there

I want to print an Envelope onto a MIDI clip and send it back to Ableton, ideally an envelope automating a VST parameter

(in practice i want to be able to automate the Envelope Decay length of a 3rd party VST using the note length of a given MIDI clip, so that the decay envelope dynamically changes according to the midi note thats just about to start, meaning every notes decay is as long as the note itself) (ofcourse this means adding the envelope retrospectively)

So far I've Read the MIDI clip into a coll and sliced out the info i need into another Coll (using live.object)

So I have a list now of Start times and Durations of notes, which I could make into a stepped Function graph x = start time y = Duration, but how could I put this back onto the midi clip as an automation envelope

any help appreciated

thanks