a) make sure your tool will not slip
b) get a longer bar

If the internal teeth break off the cup, support the non-drive side of the bb shell with something that will allow the axle to pass, and strike the other end of the axle.
Hit it like you mean it.
What you want to happen is the part of the assembly on the other sode of the now-broken cup to fall out the other side.
Then you remove the broken cup with a hacksaw.