Just use a different offset for each, G54 G55 G56 G57 G58 G59, this is the standard number of offsets, and I'm sure Mach4 has a lot more than this that can be used, each one can be used in your program, and each one would have the fixture offset X------ Y--------- positions set
You can also use just ( 1 ) offset G54 and just have a G90G0 X0.0Y0.0 next where ever it might be G90G0 X3.5Y2.1 Etc moves to each fixture position
If you want each offset to be a 0.0 position then use a different offset call for each G54/G59