It can be done, but it would involve you (or someone) writing the kinematics for CoreXY. There is a section of the code in the kinematics.c file for inserting the inverse kinematics for conversion from cartesian to non-cartesian dynamics. There are a limited number of machine cycles so the transformation would have to be pretty efficient (running in less than about a millisecond, altogether), but I suspect a CoreXY transformation on only X and Y should be possible.
I hope this helps – given that there is no native support for this right now.
Alden