Here is a nice little script that is placed in a triggers on enter stage. If the pc has a local int set to whatever it will send them to wherever you want... to an ambush... or to save the world... again... Whatever.
[script]
////////////Created by David copyrighted by Bioware


void main()
{
object oTargetObject = GetObjectByTag("V1");// Now looking back I am not sure if this is needed
object oPC = GetEnteringObject(); // declares the object oPC as whoever is entering.
int iJoinCov = GetLocalInt(oPC,"covjoin"); // now checks for the status of "covjoin" on the oPC change covjoin with what you want.
if (iJoinCov == 1) // now the check
{
location lTarget = GetLocation(GetWaypointByTag("WP_")); // replace WP_ with your custom waypoint.
AssignCommand(oPC, ActionJumpToLocation(lTarget));
}
}