Does mecanim humanoid work with spline IK

I have a character whose arms and legs are setup as spline IK in Maya. On importing the humanoid rig into Unity, I add the additional spline bones to imported FBX's Animation->Mask->Transform. Unfortunately the posed arm is not curved like in Maya but segmented at the elbow. This works correctly if I use a Generic rig (only if I re-import the FBX but I am guessing thats a bug). Am I missing any steps in the import setup?

In case this is an inherent limitation of the default Humanoid rig import, can you please suggest any scripted work around?

Thanks!