Wow, that looks like exactly what I was talking to Freddie about a few months ago before my Warcraft break.

In my case I play two accounts on the same PC with exact same window positions and UI layouts. I use pitbull to sort the party frame alpha on both and the party frame includes the player. (All 5 names are in party frame including my current toon). The game window is in windowed mode and lays over one another with the tank class in front (warrior) and healer (priest) as slave. I was trying to get this to work using the mod "Clique" which allows you to bind spells to mousekeys+modifiers. Right click might be flash heal, shift+rclick would be greater heal, mouse4(thumb button) would be power word shield. Since both windows overlapped the mouse cursor was already in the proper position, it just needed to pass the click and back then, the HKN had a delay and it would be unreliable, I also had some issues with mousebinds. It would work with mouse position + a hotkey, but that reduces the intuitiveness of it being a simple point and click method.

However, it looks like you might have this figured out! I will have to check into it and reacquaint myself with HKN.