I don't think this is necessary. I can do this in `lua_cocos2dx_physics_manual.cpp`.
And, you don't need to use `EventListenerCustom` to receive events, you can use `EventListenerPhysicsContact` or it's subclasses instead. Lua banding for these listeners haven't finished yet, I will commit a PR for this recently.
And `event` param doesn't needed in `EventListenerPhysicsContact` callback functions, I will fix this after this PR is merged.
BTW, great job for this PR, thanks!