Looking for a plugin that adds a note played by another instrument to the top of a chord.

ANYWHERE on a keyboard, not divided to zones a series of chords is played, and the top note of the chord should be replaced or doubled by another sound.
In Ableton I can create a Instrument Rack and assign a 2 synths into it. Without any changes both instruments will be layered. So, I thought that if I will be able to make one of them follow the top priority (no sound below a pressed key sounds, only a key above can trigger another sound), this way that instrument will play only the top note of the chord, while the second instrument will play the entire chord.
I do see some synths with a bottom note priority, I guess it is not too difficult to reverse it.
OR, maybe there is a (LFM) plugin that simply manages 2 instruments the way that one of them plays only the top note.
Please let me know.