There's an easier way to achieve this. Make the primary driver (the abs rotations in this case) a keyed dependency (ValueOp) Only give it 2 keys. The "one" value will go where ever the joint needs to be rotated to and the zero is usually zero. (You can get more tricky with this by fiddling with the active range of the keys)

The point is that when the joint is rotated the other (wrong?) way the the values will be zero. So zero times any thing is still zero.

The OpTimes will be set up the same way

If you look at the dependencies for LaFemme as an example there are several 2 axis JCMs on her shoulders. JCMlArmFwdUp is a example that one axis is negative.

Keyed Dependencies on the driving dial ...

The Value ops on the controlled morph ...

I recommend setting the scalar for the OpTimes so it will be 1.0 at the desired rotation. So 1 divided by what ever the rotation is. In this example it would be 0.022. That way all the "makes my brain hurt" type math is done at the lowest possible level. You don't have to figure out what 1 / Xrotation / Yrotation is.

Pay no attention to the bottom two dependencies. Those are for making the it possible to shut off JCMs from a master switch in the body and an override for manually controlling the JCM when it's disabled.

P.S. All this is a highly exploited BUG. It's just that it turned out to be a really useful bug. It has since become a legitimized and evolved into a feature.