Can I midi-map a parameter that is in the envelope dropdown?

[mbira]

I have a synth in Reason that is running as an exterlal instrument. I'd like to be able to use a foot pedal to control a filter there. I can see the parameter and edit in the envelopes (in ableton) if I create a midi clip, but I don't see a way to modulate it while I am direct monitoring myself playing. Can I do this within ableton?