I'm guessing yes here. We did this back in the day, before fancy CAD/CAM, to mill cam tracks. Let Excel calculate the path and output the text file. Gcode is nothing more than text, so anything that saves a text file will import to Mach4 gcode. If you can write Gcode in Notepad, you can surely do it in Excel!! The trick, of course, is getting the output format correct.
Tom