Alternative to splineIK for Twist + Bendy Setup?

Currently I am rigging arm twists with an IKspline that goes through a joint-chain.
There are 3 xtra joints driving the NURBS_curve, the middle one is bending the forearm here.
For getting the right twist I use Advanced Twist Controls in the ikHandle’s attribute editor, with 2 locators driving the twist at the start and end of the chain.

I want to make my rig Rumba compatible, but they don’t support advanced twist ctrls for ikSpline. I’m at a loss on how I could get the same behaviour with a different setup…

If I use orientConstraints then how do I get the bendy behaviour when translating the bendy ctrl (and they keep flipping :frowning: )?
If I use an ikSpline how can I drive the twist without the AdvTwCtrl?

I also looked at Chad Vernon’s approach but it’s a little too high-concept for me to understand :confused: and it still makes me wonder how to marry that with an ikSpline…