Actually, you can detect hitboxes by using the paintcan particles. There was a script for it... let me find it...
EDIT:
Yes, here's the code for checking for a hitbox with hitboxes.cs (assuming this is in a ProjectileData::damage(%this, %obj, %col, %pos, %etc..,) function)
%hitbox = getHitbox(%obj, %col, %pos);
if(strPos(%hitbox, "headskin") > -1)
{
//do stuff for headshot
}