JSONP with Rails

Question

I'm trying to retrieve JSON data from a remote site with Rails/Prototype.

I've found that there's a branch of Prototype that has an Ajax.JSONRequest() function. I can't get this to work.

jQuery has a $.getJSON() function, but I'm using some Prototype functions and I'd rather not switch to jQuery or use no conflict mode.

What am I missing? It seems like this would be easily done with Rails or Prototype.