You can handle the cellclick and add the preview row to the current selection.
Here is a sample.
If you want the selection to be navigated using the Arrowkeys, then you can use the technique shown in this KB:
http://www.syncfusion.com/Support/article.aspx?id=10496
We are planning to change the selection mechanism in the groupinggrid to be based on record. This will be easier after that. For now, you have to handle this way.