Well something ive been thinking about trying but not actually tried yet is as follows.
Since your healer is on your 2nd computer you could set up the 2nd computer to share mouse movements/clicks to mimic your first one, set both mouses to the same sensitivity and also same screen resolutions (Not 100% sure resulution is required, as long as you scale the mouse sensitivity it shoulndt be).

Then install a click casting mod such as Healbot or even Clique on both computers, however only set up the actual heals on the healing computer (e.g on the main computer have healbot set to do nothing on any clicks, then on the heal computer have left click cast a flash heal, right click pws, shift right click greater heal whatever). You should be able to click /rightclick/shiftrightclick on your main screen and have the 2nd computer be doing the same click on that mod for whoever you are trying to heal.