I can’t remember if I had to wire it up manually, but under Library → Playing Techniques, in the Common category there is Laissez Vibrer (l.v.). Just make sure the Playback Technique is set correctly (to Laissez Vibrer).
Then you can just add that to the expression map (on events: CC64/127, off events: CC64/1). See this thread:
It a different technique, but the procedure is identical.