jemungo, on behalf of the whole forum I'd like to apologise for our lack of clarity.
Create the unit
Create the trigger
Press F2 or click on Groups
Group the trig to the dude (or is it the dude to the trig ...) as if the trigger was just another dude.
Admire the light blue line between the dude and the trigger
Open up the trigger and you will find some new options in the activation field - group leader, any member etc.
Hope that does the trick.