The same question was asked by your colleague James Blair (Company: Napier University) and I have already answered it in his support ticket. For your convenience I pasted the main part of my answer:
"I am not quite sure that I understood your requirements, but I suppose that you need to initially hide all items and then begin showing them from the top of the page. If this is your requirement you can set the InitialItemIndex="-1" in order to achieve the desired result. In case that ......"
I hope this helps.
the Telerik team