The slickest way I have seen was just posted here: he took a tap and ground the tip of it back until it was just wide enough to grip the flange, and turned it into the shell and tugged it out.
That's better than my way: I use a tiny drill bit on an angle to the shell, drilling into the body and thru the flange so I can get a pick on it, bend it inward, then nab is with (new) needlenose pliers to pull it out. Sometimes it is possible to just get an edge of it with something pointy and sharp (I have also used a small pocketknife's blade for this) and bend it inward so it can be grabbed and pulled out.