If you're puzzled about the implementation, I invite you to inspect the JavaScript code! And if you disagree with my implementation, I'd be interested to know what you would do differently.
My statement was conceptual. Boolos himself suggests that we ask if X is random to get to a solution (though in a more complex iff statement). But being able to ask if a source is random seems unreasonable, though without that capability I can't say if there is a solution.