NodeLabelDraggingTool - how to set initial label offset?

I’m using the NodeLabelDraiingTool, as per example at http://gojs.net/latest/extensions/NodeLabelDragging.html. I want to set the initial label offset (i.e. position relative to the node) from the Diagram Model, it being potentially different for each node, but cannot see how to do this. Could you show me how?

Thanks,
Robert

Set the alignment property on the node data object. There is already a TwoWay Binding on the alignment property of the node’s TextBlock label.

Move a node label manually, click the Save button, and see new value for that node data’s “alignment” property.