Accessing/(re)using already-existing clip envelope data

this is really an Ableton question, but I’m working on a Videosync project, so I’m going to ask here:

I have created a complex set of clip envelopes in Session View.

I now want to use some of those already-existing envelopes to control other parameters, in order to create convincing audiovisual ‘sync’.

Can anyone explain a good quick way to do this?

I have tried creating a rack, and mapping the already-enveloped parameter to a Macro, with the idea that the Macro can then be linked to other params. Unfortunately, this has the effect of hijacking the parameter away from the envelope. Can I restore the envelope somehow, and get it to control the Macro?

I feel sure this must be possible, but I can’t find a work-round. Everything I look at online about envelopes and mapping is approaching it the other way around. This is probably a dumb question, but thanks for any help.