Apparently this seems to work, but not sure if it is the best way to do it. Need to do the below in the SelectionChanged event of the GridView. I'm setting the SelectItem to null so that it triggers the selectionchanged again when again clicking the selected row.
(!e.AddedItems.Any()) e.Handled =
var gridView = (RadGridView) sender;
var selectedRow = gridView.ItemContainerGenerator.ContainerFromItem(e.AddedItems)
selectedRow.DetailsVisibility = selectedRow.DetailsVisibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
Hope this helps someone else!