I am not sure I have managed to grasp your scenario completely. Do you want to enforce a field to be mandatory selected, or you want to select a newly added item to your custom list?
Could you provide us a sample project or a bit more info on the topic? The best way to assist you would be via simple project demonstrating your case and explanation of the steps you still need to achieve.
I have changed support tread type to general feedback so you could attach a project.
I am looking forward to your answer.
the Telerik team