Automation Of A Sample's Envelope Release Point

I want to be able to automate the release point of a samples envelope over some parts of my song. Looking in the automation section of renoise i can only see a box for volume automation which may be relevant, however this just automates the overall volume of the sample, not the envelope’s release point as i wish. Anyone know how i can achieve this?
Many thanks

thats not possible at the moment.

looza is right.

however, in case you don’t know, you can still decide when release will occur: switch “sustain” on in the instrument envelop, set the sustain point, then input a note-off command (CAPS-Lock key) on the row where you want to turn sustain off.

sorry if you already knew this

If you just wish to make a smooth release of an instrument :

using the note-off suggestion of it-alien, create an envelope with a sustain point at step 0 (and a small envelope going down) and then use the note-off command (or the Fx (note cut) command in the volume/panning column). this way you can trigger the release with tick-precision.

or maybe just explain what you are trying to do, possibly we guruhs can come up with some solution :D