Mark,

Offset Mixing is what you need. I obviously haven't got my 18mz in front of me so I will try to explain from memory.

Goto program mixes, by default its a normal type mix so you need to click the yellow button to change it to offset mixing.
Go into the mix and then you an assign the mix on/off to be the retract switch.
In the offset mixing you can change the off/on position for any channel, the delay moving to each point and the speed.

I have complex sequencing on F104, all done by this method and can send you the program if necessary.

Geoff.