...When the G code is running the X axis I need to be able to 'direct input ' commands to the Y and Z axis without stopping the program running....
It doesn't work like this. You can't have a continuously-running axis and then do motion on other axes.
Without being terribly rude, you need to read up on the concept of coordinated linear motion and understand and accept what it means.
What you want to do is certainly possible in a way, but not using 'standard' Mach. One route to go down might be to set up X as a step-and-direction SPINDLE. You could then control X- with G03/G04, with the S-word in reality being the F-word and do what you like with Y- and Z- in the meantime.