I suppose you could use Perl to flag/unflag players when they zone in.
Here is an example using an NPC to do it:
http://www.eqemulator.org/forums/showthread.php?t=25874
Quest wiki entry:
http://www.eqemulator.net/wiki/wikka...uestCheatSheet
Look for sub EVENT_ENTERZONE and quest::pvp. I've never tried to write a script that combines those two elements, so I can't say for sure that it would work but it is something to get you started.