I am not sure that it is possible to solve this issue with blueprints. But I found a workaround: I transform the viewport with a material post-process and fit it to the position of the widgets on the screen:
The post-process material will look like this:
Here’s what it looks like on the screen:
You will need to do some math to get the correct results on the screen.
However, this approach has a significant drawback: you need to perform reverse calculations to interact with scene objects, with Line Trace or another way.
My Quiet Docking System has such a viewport fitting: