A simple scripting method using a pseudo heartbeat can reset the map to blank (with the exception of the immediate area surrounding the PC.
Void Unexplore(object oPC)
{
if (GetLocalInt(oPC, "Unexplore"))
{
ExploreAreaForPlayer(GetArea(oPC), oPC, FALSE);
DelayCommand (6.0, Unexplore(oPC));
}
}
You wouldn't want to run this all the time, but if you have selective need for it you can put in toggles to turn it on and off by setting and deleting the Unexplore int on the PC.