The best I came up with for different targets was this:

/castsequence [target=mouseover,exist] reset=15 blessing of kings, blessing of salvation, blessing of salvation, blessing of salvation, blessing of salvation

This is so that I can cast Kings on my tank, and Salvation for the other 4 toons. I just move my mouse to the toons in order.

Of course, this would only work for your main that you are controlling with the mouse to do all the mouseovers.