Well, when you create a unit, you need to specify what group he is going to be put in, right? So you could probobally put down a unit, give him a S&D waypoint, then put this in his init field:
group1 = group this; deletevehicle this
Then you create your new unit into group1, and set the S&D waypoint onto his location using the setwaypointpos command. Thus, when he is created into that group, he will immediately start doing that group's waypoints.
I've never worked with created units myself, but I would think this would work.