Not as hard as you may think, write a program to do one part (this will be the sub program),then just move in x-y to do next part and call sub program again.
So lets say you call right rear corner of fixture your part home,then you call out sub program and make the part,then when you go back to your main program you simply move in x-y.
G40 G49 T2 M06 (DRILL)
G00 G90 G54 X0 Y0 S500 M03 (PART ZERO)
G43 H02 Z2. M08
M98 P2 ( CALL OUT SUB)
G73 X0 Y0 Z-1.375 R0.1 Q0.3 F5.
X-1. (MOVE TO 2ND PART)
AND SO FORTH
on your machine you may have a differant m to call out sub program or go back to main,this would be for a haas.