Build step 1800_copy_vms_into_raw now looks good in theory but untested.
https://github.com/Whonix/Whonix/blob/master/build-steps.d/1800_copy_vms_into_raw
I did not put qcow2 images into packages (yet) because I am not sure how to implement this and implementing above is quicker and easier. Maybe future work.