difficult flattening

[micheus]

It's hard to imagine the geometry of your model, but I tried to guess how it looks like.

...and I also think you will not have a solution, but I'm going to show how you can flatten faces and preserve those vertex in the top-corner in their location.
This way I think you can try by yourself using your model and see if you find a solution.



In the final result I replicated the steps for the right pentagon - which will deform the left one. Then I repeat the process once for the left and right.