I wonder if some kind of a smart kinematic mixer would work here.
Imaging an electronic unit with three stepper inputs (step, direction) for cartesians channels X, Y, E, and three stepper outputs for the kinematic steppers A, B C, such that pulses the input kinematics are mapped to pulses of output kinematic. Do thinks like this exist?
Somehow related to the electronic gear idea in this video (though it's a single channel) https://www.youtube.com/watch?v=FTs9GygRQ-U&list=PLDlWKv7KIIr90ZZ7Zqt-ge5nVVdS3WVgg