You can setup a different profile for just the laser in Mach3 so the PicConvert uses different step & direction pins for running the Z axis gcode commands from Aspire or PEP6 to control the laser. In that profile set the A axis step & direction pins for jogging the Z axis stepper to adjust the focal height instead. You will have to change your steps per, velocity and accels in Motor tuning for the Z & A axis changes. You don't have to remove Z.
You can create a new profile by cloning your router profile, name new (laser?) and make your settings changes.
When you want to run your router, open the Mach3 profile for it.
I would help you with the Post Processor, but I don't use any Vectric software programs to even know where to start.