Well, you're doing the headswaps right, and probably about as efficiently as you can, from the sounds of it.
One thing is that the Dota girls are probably always going to look weird, just due to those model styles, and how the models are built. The don't exactly have the best textures, or rigging, as far as I know.
Only thing I could suggest is a mess of postwork in Photoshop if you're just doing a single render.
That, and like you already do, just hiding the bad areas with the camera angles.
Hope that helps. :)