I was integrating with a client's API which used a blend of JSONP and XML. Sencha Touch 2 does not have a native way to parse this, so I extended XML reader to make a 'jsonpx' reader. Hopefully this will help someone who might run into the same situation.

Code:
Ext.define('app.util.JsonpX', {
    extend: 'Ext.data.reader.Xml',


    // Set the proxy alias
    alias: 'reader.jsonpx',


    parseXmlString: function (sXml) {
        // If the specified XML document content is a string...
        if (typeof sXml == "string") {


            // Create a reference to the XML document parser.
            var oParser = new DOMParser();


            // Return the reference to the XML document.
            return oParser.parseFromString(sXml, "text/xml");
        }
        else { // XML document content is NOT a string...
            // Return the specified XML document since it has already been parsed.
            return sXml;
        }
    },


    /*
    * override
    * @param {string} response the response to parse
    * @return {xml} the XML data that has been parsed
    */
    getResponseData: function(response){
        response = this.parseXmlString(response);
        return response;
    }
});
To use, place the above code in a file [app root]/util/jsonpX.js

Inside of the store you are using, make sure to include and declare it as the reader. For example:

Code:
Ext.define('Year', {
    extend: 'Ext.data.Model',
    config: {
        fields: [
            {name: 'id',  type: 'number'}
        ]
    }
});


Ext.define('smtp.store.PartsFilterYear', {
    extend: 'Ext.data.Store',
    requires: [
        'Ext.data.proxy.JsonP',
        'app.util.JsonpX'
    ],
    config: {
        autoLoad: true,
        storeId: 'PartsFilterYear',    //    ref to bind inside views
        model: 'Year',
        fields: ['id'],
        pageSize: 100,
        proxy: {
            type: 'jsonp',
            url: 'http://somedomain.com/someapi',
            reader: {
                type: 'jsonpx'   //declare reader
            }
        }
    }
});
This code was inspired by a piece a found for Sencha Touch 1 - http://www.sencha.com/forum/showthre...gProxy-and-XML

Hope this helps.