Dell seems to have made the leap of faith and did away with legacy boot.
From what you are saying, the problem is the BIOS incompatibility, so if there is any solution, it is the one you mentioned yourself:
Suggestions exist on how to "hack" GRUB to force the system to boot seems to exist
I may be mistaken, but it will be difficult for someone to help you in this case, you have already found the source of the problem and a possible solution, there is no more that can be done ...