I have drawn some volume automation envelopes, but I've realised that it would be better to have these volume adjustments modify the signal before it hits the compressor plugin I'm using, rather than after.
 
But there doesn't seem to be an option that would allow me to reassign this envelope to a plugin parameter.  Anyone have any clues about how I could do this, or a workaround to achieve the same effect?
 
Thanks!

right-click on the envelope,then re-assign...
 
hth
 
martin

What you want to modify is the Gain trim.
This is the signal that feeds the compressor. I would personally just copy - paste the automation from my volume lane to my gain lane and then remove the volume lane.
 
I would however expect to make some adjustments. Gain and volume are 2 different things and one really wont substitute the other.
have you tried simply turning the compressor ratio down ? or the input feed to the compressor ?