Actually, it is possible. HOWEVER, I do NOT suggest using this with an NPC you actually intend to use for quests, because it may cause issues with triggering various sections of the quest, if not all of it. Using this to add life to a zone would be a nice touch though. Maybe have some crazy npc that repeats what everyone says.
Code:
sub EVENT_SAY{
if($text =~ /$text/i){quest::say("$text?");}
}
That's it. Tested it just now and it works.