If a non-automatic way is enought, perhaps you can set waitafterconvert=true, so, when the converting process stops, in waiting user action, you can copy the generated cubes and then continu with the converting process....
Quote from kmakemultires.config
Code
.....
# waitafterconvert
# - wait for keypress after converting to cube
# - this allows editing the cube faces before final processing
#
waitafterconvert=true
.....