How to get C++ "this" address from registered instances in Lua back to C++?

[shohnwal]

Lets say i have a C++ Luainterface class instance that i want to register in Lua:
When registering an already created C++ class instance ina Lua via

void Luainterface::registerMyself() {
    this->lua["CPPinterface"].SetObj(
        *this,
        "cpp_dosomething", &Luainterface::cpp_dosometing
        );
}

and working with the object in Lua and i want to pass the class instances address (or pointer) back to C++ so i can access the instace via a converted C++ pointer, how would i do that?

To be more exact, how do i access the "*this" element in the (in this example) CPPinterface table so i can pass this address back to C++ and work with it?
The other elements (like &Luainterface::cpp_print) are all associated with a string and it's easy to access them, but i can't figure out how to access the "*this" element containing the objects address.

So far i've been creating extra class member with a pointer on itself

class Luainterface {
Luainterface() : cpp_thispointer(this) {} //constructor
//other stuff
Luainterface* cpp_thispointer; //class instance member pointing on itself
}

and register it in the SetObj function in addition to the rest

void Luainterface::registerMyself() {
    this->lua["CPPinterface"].SetObj(
        *this,
        "cpp_this", &Luainterface::cpp_thispointer,
        "cpp_dosomething", &Luainterface::cpp_dosometing
        );
}

It works by converting the Lua table element in C++ back to its originaltype

Luainterface* pointer = (Luainterface*)lua["CPPinterface"]["cpp_this"]()

but it's a bit cumbersome to have that extra member element and extra lua function to register and remember.
Would it be somehow possible to access the "*this" element (used during the objects registration itself as seen in the example above) in Lua so i can send it back to C++ and convert it back to a pointer or address? Or does the "*this" element used above not end up in the Lua table at all and we have to do something like extra entries/members, like i have done above?

PS: Thank you for creating Selene, it's quite awesome! :D