protected override NodeBase PrepareLookupNodes()
{
  VirtualRootNode lookupRoot = base.PrepareLookupNodes() as VirtualRootNode;
  lookupRoot.GetNode += new GetNodeHandler(GetNode);
}
private NodeBase GetNode(NodeBase sender, int position)
{
  // here you can provide custom drawn node, as work in the virtual mode -  
  // see the Virtual Grid sample for the different ways of custom drawn nodes
  // usage
}