Hello,
I'm putting this out there because I can find no useful information online. From my understanding, to run Mountain Lion on an unsupported Mac with 64-bit EFI, you need a patched boot.efi that supports booting the 64bit kernel (I know this is not required on Mavericks and newer). For an unsupported Mac with 32-bit EFI, you need a patched boot.efi as well, but a different one. I have tried using many different copies from multiple patchers with varying degrees of success. But there's one thing I haven't been able to find: Where the files come from. If anyone can track down two actual working files *and* where they come from (MacRumours post, GitHub repo, anything) I'd appreciate it. If you're a developer of some kind of patched boot.efi file, please contact me directly. Thank you.
Edit: Found out they were compiled from Piker Alpha's macosxbootloader repo on GitHub. Still having issues with them but I have located the source of them at least!