Made a basic (and rather bad) shoulder rig to test an idea. I'd post pictures but the camera batteries died and I haven't gotten new ones yet. But it seems to have mostly solved the problem of the upper arm not staying straight and/or hitting me in the head. Up/down movement will likely end up being limited, but forward/back should have a good range and allow some rotation.

Using a shoulder rig also let me try out moving both arm pieces at once, which felt both odd and cool. It will take some getting used to when I make a more solid arm, but it should hopefully work out well with practice. Even better if/when I get to work on articulated fingers.

I'll get pictures up when I can, but for now I'm trying to figure out the best way to do Soundwave's chest and legs. Looks like I may need to use stilts to give the lower leg a bit more length :S