The Wikipedia article on Continuation says:
"In any language which supports closures, it is possible to write programs in continuation passing style and manually implement call/cc."

Either that is true and I need to know how to do it or it is not true and that statement needs to be corrected.

If this is true, please show me how to implement call/cc in Lua because I can't see how.

I think I'd be able to implement call/cc manually if Lua had the coroutine.clone function as explained here.

If closures are not enough to implement call/cc then what else is needed?

The text below is optional reading.
P.S.: Lua has one-shot continuations with its coroutine table. A coroutine.clone function would allow me to clone it to call it multiple times, thus effectively making call/cc possible (unless I misunderstand call/cc). However that cloning function doesn't exist in Lua. Someone on the Lua IRC channel suggested that I use the Pluto library (it implements serialization) to marshal a coroutine, copy it and then unmarshal it and use it again. While that would probably work, I am more interested in the theoretical implementation of call/cc and in finding what is the actual minimum set of features that a language needs to have in order to allow for its manual implementation.