I asked a similar question and never got an answer, so I kept looking into it myself. From what I can figure out, it's possible to do with a floater (one of the floater advanced options is to do a different action on right or middle clicks):
1) Create two floaters (say actions 111 & 112)
2) Set both to the same healing spell
3) Set #112 to use you as the default target, forced, and hide #112
4) Set #111 to use action #112 on right-click
5) Position #111 however you like
That should set you up properly; you'll cast the spell on your target with a left-click, and cast it on yourself with a right-click (technically you could even set it up to use a different healing spell on you than on other targets, but that could be a bit confusing).
If you find a way to do something similar with a bar, please let me know
