Ext.data.GroupingStore and Presto.extjs.ServiceStore - grouping data from a Service Store

Hi:

I am trying to create and expandable/collapsible grid using data that has been obtained from newPresto.extjs.ServiceStore.

        this.dataStore = new Presto.extjs.ServiceStore({
            connection: conn,
            request: this.request, // JUMP request
            remotePaging: !disableRemotePaging, // to include a server side pagination
            record: "/xml/record", // the repeating node
            columns: ["WBSElement", "Type" ,"Customer", "Enterprise", "Infrastructure", "Software_Engineering", "Workforce"],
            recordId: "WBSElement", //  unique identifier for the row
            pageLimit: this.rowsPerPage
        });

The result format from the service is an XML.  I then need to use an Ext.grid.GridPanel, and the store will be a Ext.data.GroupingStore.  The groupingstore data field expects an array, is there a way to feed it the dataStore? If not, what is the best way to display the data from the DataStore to create groupings (expandable/collapsible) rows based on groups?

Thanks for the help,

Farzana