I don't know how the damaged portraits actualy work in BG (this red bar rising up according to the damages), so I couldn't speak about implementation.
But yet, in order to save some time, perhaps you could try and use the already existing BG1/BG2 portraits?
Also, I can't help but think that you probably could reuse some of your "wound" layers according to similar shapes of specific portraits. For instance, whenever Imoen had the same location for her eyes than (let's say) Jaheira, you could possibly use the same "black eye" layers for both.
If feasible, this would save your time too...
Anyway, I personaly find the idea fresh and funny.