Ext JS 4.1 introduced changes that allow one to pass store/reader configuration data as metaData from the server. This allows for changing configuration on-the-fly at runtime. CFQueryReader, for parsing ColdFusion's JSON response of it's native query objects, now supports this great new feature.
Documentation can be found at the CFQueryReader site (thanks to Ed Spencer, who I think wrote that documentation for the JSON reader, for which I borrowed heavily). You can also see a demo of this in action (Firebug is your friend). Full source code can be found in CFQueryReader's GitHub repository.