It seems like I do not understand completely you scenario. Basically you can add new items to any item at any time if you are not using data binding (which as I understand is your case).
Can you please clarify again what the exact problem is - when you are not able to add the new items?
Sorry that it takes so long to identify the problem. I hope that with the next iteration we will be able to help you solve the issue.
the Telerik team
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