This solution came up as a hit on Google and I understand the purpose of it however I found a simpler solution.
In the widget you are drag/dropping, use the Event on Drag Cancelled override.
Then, use a 0.05s or some value like this as a delay with a boolean to determine if your drag was holding onto a widget.
What happens is that the action is cancelled and the delay given allows the system to recover the position of the cursor, and then it can determine what is under it. In my use-case I used a trace since I needed something else.
If a value in the delay is of 0.01s, depending on FPS, the event may misfire, so use a value where people cannot see the difference, under 0.1s.
In practical terms, this is easier to implement with less overhead and less places to debug.
It’s not an exact method, but if your usecase is to drag and drop from a widget to world space, this works fine.