Cross-domain AJAX (JSON-P) with Ext JS

Hi All,
I have this web service, with JSON

/api/whatismyip.php

Code:

---

{"ip":"66.249.65.115"}

---

and with JSON-P

/api/whatismyip.php?callback=functionName

Code:

---

functionName({"ip":"66.249.65.115"});

---

The client-side uses only JSON

/examples/whatismyip.html

Code:

---

Ext.Ajax.request({
        url: '/api/whatismyip.php',
        success: function(response, opts) {
                var obj = Ext.decode(response.responseText);
                //console.dir(obj);
                Ext.get('loading').fadeOut();
                Ext.MessageBox.alert('IP Address', obj.ip);
        }
});

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Do you know a way to use JSON-P with Ext JS ?