mecanim, adjusting character stance with mouse input using c# script

Hi there, I've started using the new mecanim animation system and I'm happy with applying various standard animations and blending animations together.

However I'm struggling to work how I could overlay mouse inputs to adjust the bone position of the character to get adjustable positions. I was hoping that the IK system would extend beyond just head, hands and feet?

Example 1: character is walking along and I want them bend their knees (lower knee joint to ground) a certain amount based on mouseinput, so as the overall character is lower, rather than having a series of different couch animations.

Example 2: character is walking along straight but aiming to the left or right it would be nice to be able to twist the upper body (and not just the head) towards the aiming direction.

I would like to experiment we all sorts of adjustable bone positions but still maintain the overall mecanim animation setup.

The problem at the moment is that I can't see how to override the mecanim animation.

Is the above even possible? Any help or example code to get me started would be extremely welcome.

Jamie.