Gotcha, Sorry, I was thinking of something else.
My suggestion would work but it wouldn't be something you can do on the fly, like you are requesting.
What I was talking about was turning on the Envelope tool for the of the clip,
The setting the Opacity to be controlled by the "Clip Position",
Then pausing the clip,
Then scrubbing the playhead of the clip to the point where you want it to start fading out,
Then adding a keyframe or node to the envelope at that point (when paused the node should be in the exact spot of the playhead),
Then turning the first or last node or keyframe down to 0.
This would get you what you were asking for, but again, not an on-the-fly solution.
Not sure if your BPM work around or a Touch Designer OSC patch would be quicker. I would think the BPM would be, as it's once less app to open and to switch back and forth on.