Unfortunately this is something you won’t be able to do too much about. The MPCNC firmware set-up will control the laser with the M106 and M107 commands . A better way to go is to use the M03 and M05 spindle commands to drive a laser. Then you just have to set up your CAD/CAM software to use a certain spindle speed with any given tool, and set the tools size to the beam diameter of your laser . The M106 and M107 commands don’t really work for this.
This would require a firmware mod to make work.