Software compensation for skew in a gantry setup

Hey all,

I've got a gantry system (used as for a laser cutter) where I've got a residual skew that I'd prefer not to remove on the gantry beam. This means that an attempt to cut a square would result in a parallelogram. I would like compensate for this in software, preferably in a way that would still allow me to use the stable branch in the APT repositories (which, AFAIK, means I can't use a custom kinematics setup).

As the compensation I'm aiming for is something on the order of;
Z_new = Z_old
Y_new = Y_old
X_new = X_old + k*Y_old

for small values of k (on the order of 1/200) using machine coordinates, I was thinking that this *could* be fixed in a relatively crude way by hijacking my commanded output/stepgen input;

net xpos-cmd axis.0.motor-pos-cmd => stepgen.0.position-cmd

with a suitable conversion (as well as handling the position feedback similarly). Does anyone here know of a cleaner/better way of solving my situation? Again, keep in mind I'd really like to be able to use the distributed package in the stable repository, so (afaik) I won't be able to define a custom kinematics setup (as AFAIK this can't be loaded into an existing linuxcnc binary).

Thanks!