Stepper drivers are so cheap (about $1 per driver now) that if milling is your use and you don’t have it set up as a printer I would suggest just adding two more drivers and setting them all to .75V. You do have to edit the firmware you choose to run, Repetier makes it very easy with a web interface to do it all before you even download the firmware, but Marlin wasn’t too bad once I found the right part of the stepper code I just told it everytime you set direction or pulse for X/Y do it for E0/E1 pins too.
I have the kit motors and I believe they are rated for 1.5A right? They don’t seem to be overheating at that.
If I add printing functions later I could also just add some TB6600 drivers for $8. The Diamond hotend in particular has caught my eye and adding it to MPCNC would actually be easier than with any of my other printers.