How to set the initial position of the node in a canvas

When I drag any element from the palette and drop it into canvas for the first time I want to fix the position of first node that is dropped. How I do this? I tried few Diagram methods but dint work for me, Please help

Thank You

The normal expectation is that when the user drag-and-drops a node, the node should go where the user dropped it, or else it should be moved by the custom Diagram.layout, which is responsible for positioning all of the top-level nodes.