I believe that the possibility of having armature manipulations via “controlJoint” blend with animations has previously been discussed and turned down, but I would like to make a suggestion, if I may.
I would like to suggest implementing such a blending by considering transformations made via “controlJoint” to be essentially a static “animation”; blending might then be achieved as with standard animations, with the blend weight being set by passing a constant to “setControlEffect” in place of the animation name.
(For my purpose which prompted me to consider this I think that I’ve found a workaround, if a slightly awkward one, but I do think that such blending has the potential to be useful.)