The thing to keep in mind is, PERS isn't really about the "joystick" which is what people really seem stuck on.
PERS simply means = Parallel Eyeball Rolling System. How HT makes those eyes rotate (roll) is up to them. People are expecting the exact same set up as the DX Joker and I get the feeling that the mechanism to move the eyes is going to be completely different for the DX Batman. Could be wrong.. but I think the mechanism will be accessed through the mouth opening (when you remove one of the swappable mouths) and it might be as simple as this:
*prepare for a fast and crude MS paint pic*
So there's a small lever accessible through the mouth opening. You simply slide the lever from left to right or up and down and it moves the eyes. Simple concept and it's just one possibility.
Thing is though, the thought of us big handed gentlemen trying to control that ish through such a tiny opening is maddening to say the least.