I'm afraid that such functionality is not supported by RadTileList and there's also no easy way to achieve the desired effect.
You are, however, free to create your own custom control
based on RadTileList, but you will need to dramatically modify it, which might lead to potential problems.
Do you need help with upgrading your AJAX, WPF or WinForms project? Check the Telerik API Analyzer
and share your thoughts.