I was playing around in single player, and my cleric was almost dead. In a flash of inspiration, I realized that I could just drain some hp from my full health dwarven warrior.. except I couldn't. This surprised me, since I've previously been able to target friendly characters with attacks, whenever an opponent is in range, or they are combined move/attack cards. So, I think it could be cool if you were able to target your allies for those few corner cases which makes you feel smart.
You can target friendlies if you hold down the ctrl key when you click on the skill. You can also turn off auto target in the options and the game will always give you the option to target your allies with attacks.