AJAX :: Callbacks And Parameters From Outside The Scope Of The Callback?

This could appear under Ajax, for example, you could have multiple objects that make a singular ajax call (say an RPC-like request) and you need to update the object that made the call during the callback with the result, but it doesn't have to be. The particular problem I'm thinking about happens to be ajax, particularly with multiple objects accessing the same ajax request (meaning I can't use a global or temporary variable).

One way that seems like it would work (just thinking about it in my head), is to create a hash, and to pass the key through the request, store the key in the response, and pick it up on the callback side. Then remove the item from the hash when done.