Try this approach.
Create a unit, give him one waypoint of type SAD (or move, whichever you want). In his init field put:
gReact=group this;deleteVehicle this
In your patrol leader's init field, add
gPatrol=group this
Now, when the trip flare goes off, do setWPPos for gReact's waypoint, setting it where the flare went off.
The move everyone from gPatrol group to gReact group, in order, with the leader first.
They'll set off on SAD at the flare point. Have that trigger spawn a monitor script that checks if they ever find anything. If they dont, move them back into the group gPatrol. They'll merrily go back to patrolling on the original patrol waypoints.
You can repeat that as often as needed, setWPPos'ing the gReact SAD waypoint whereever the trip flares go off.