Thank you for writing.
This scenario is certainly achievable. The easiest way to achieve it is to set the Enabled property, of the items you don't want to be selectable, to false. You can use the VisualListItemFormatting event to determine which items to disable. Here is a code snippet which demonstrates this:
sender, VisualItemFormattingEventArgs args)
args.VisualItem.Enabled = ((MyPositionType)args.VisualItem.Data.DataBoundItem).Flag == Flags.N;
I hope this will help you. Should you have further questions, I would be glad to help.
the Telerik team