Why not :
- find a glass ( windows glass ) small company that agrees to do the precision cutting ( and offers a reasonable price ).
- once found that, find and buy a replacement glass ( better than using plexyglass imho ) for maybe a 10" tablet... that would actually allow to : 1) obtain 2 or more spare glasses and 2) allow for cutting issues
- use a phone repairing to do the swap, you put the material
On a side note, car glass repairing shops use some tricks to fix scratched and even cracked windshields.
I wonder if they could apply the same method to the phone glass...
On a side note, IF the first method works, I think you would find people interested in the spare screens...