groups fx

hi guys.. i've a question for someone that use this kind of fx
the question is:
in my rig i have 3 truss with a different number of the same fixture (i.e. claypaky mythos or simply a spot light)
truss n.1 has 7 spots, truss n. 2 has 4 spots and truss n.3 has 6 spots.
how can i make a fx where the fixture is divided by truss?
in example a dimmer fx:
1 on 2-3 off
1 off 2 on 3 off
1-2 off 3 on
and so on...
thanks to all!