Making DTSs 'Snap' together

For my game, I am going to include an edited version of the World Eitor so that end-users can create custom content.
For building ciies, etc. I thought it would be a good idea to allow shapes to snap to eachother automaticall, to confirm that there are no akward-looking scenes. I should be able to add a custom node to each shape to allow this, but I want to know if anyone had done this before or has any ideas?

Thanks