I am a bit confused about whether you need the shapes to be always in the view-port, or you just want to have a visual distance (let say about 5 px) between the shapes and diagram border?
If you just need a padding, you could remove the diagram border and place the whole diagram inside a border element. Then apply the necessary margin to the diagram.
If you want all shapes to be always in the view-port you will have to restrict the view-port (Position and Zoom properties) when panning and zooming.
Could you please elaborate a bit more on your scenario if the provided information does not help you?
the Telerik team