Сам спросил, сам ответил
EWreview.combo.Rate = function(config) {
    config = config || {};
    Ext.applyIf(config,{
        name: 'name'
        ,hiddenName: 'product_id'
        ,displayField: 'name'
        ,valueField: 'product_id'
        ,fields: ['product_id','name']
        ,pageSize: 20
        ,url: EWreview.config.connector_url
        ,baseParams: {
            action: 'ew/getlist'
        }
        ,typeAhead: true
        ,editable: true
    });
    EWreview.combo.Rate.superclass.constructor.call(this,config);
};
Ext.extend(EWreview.combo.Rate,MODx.combo.ComboBox);
Ext.reg('ewreview-combo-rate',EWreview.combo.Rate);