Sorry, thought you were talking about the custom hunting missions quests.
For the actual quest system then you'll have to change a bit of source.
mob.c
if( sd->status.party_id )
map_foreachinrange(quest_update_objective_sub,&md->bl,AREA_SIZE,BL_PC,sd->status.party_id,md->mob_id);
You'll need to make it something like:
if( sd->status.party_id )
map_foreachinmap(quest_update_objective_sub, md->bl.m, BL_PC, sd->status.party_id, md->mob_id);