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

Hi All,
I have this web service, with JSON

/api/whatismyip.php

{"ip":"66.249.65.115"}

and with JSON-P

/api/whatismyip.php?callback=functionName

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

The client-side uses only JSON

/examples/whatismyip.html

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);
	}
});

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