Clamp joint rotation with mecanim´s muscle system?

I´m having a hard time limiting the joint movement for my characters (Quaternions are hard to clamp, and euler can´t have negative values, I couldn´t find a single code that worked).
I want this for my IK system, to avoid unwanted rotations, pretty standard stuff. I even thought of phyisics character joints, but this isn´t a ragdoll, and I don´t have a rigidbody for each limb.
Mecanim seems to have this feature build in though: "the muscle system". It allows you to limit rotations and preview the result, ain´t that wonderful?! but for some reson the people that design it aparently didn´t understand why they had to make it. The only use this is currently having is for retargetting animations, who knows why they didn´t extend the functionality. Is there any way I can see how this muscle clamping work? or is there a way in wich I can get this "muscle" restrictions to work with IK? (the latter being the prefered one). I´m thinking why redoing the whole thing when you have this already built in.
PS: I know that you can limit rotations with an asset (final IK), I´m looking for a different solution.