You don't, and i don't even think there are any third party apps that would show mob ids on widescan. But there are programs that will let you view mob ids when you target them, so if a listing in wiki says "PH ID is 139" then you could use widescan and a program to make sure you're killing the correct PH.you figure out which one is the place holder though trial and error, or you can just look up the mob and hope someone posted it.
Thats so much work! I should have known nothing is that easy. Thank you :D