Writing a recursive function without naming it is a problem that is as old as computer science itself (even older, actually, since λ-calculus predates computer science), since in λ-calculus all functions are anonymous, and yet you still need recursion.

The solution is to use a fixpoint combinator, usually the Y combinator. This looks something like this:

(y => 

  y(

    givenFact => 

      n => 

        n < 2 ? 1 : n * givenFact(n-1)

  )(5)

)(le => 

  (f => 

    f(f)

  )(f => 

    le(x => (f(f))(x))

  )

);

This will compute the factorial of 5 recursively.

Note: the code is heavily based on this: The Y Combinator explained with JavaScript. All credit should go to the original author. I mostly just harmonized (is that what you call refactoring old code with new features from ES/Harmony?) it.