AFAIK, you can't upgrade a Mac's firmware to UEFI 2.x, and if you could, there's a good chance you'd have problems booting OS X from it.
You might be able to use a "software UEFI" implementation, such as UEFI DUET, on a 64-bit Mac. I wrote a Web page about this technique on conventional PCs. Since Macs look like such computers when they boot Windows via Boot Camp, there's a chance you could get that approach to work on a Mac; however, my limited understanding is that an MBR (regular or hybrid) is required to activate a Mac's BIOS compatibility mode, so this might be a wild goose chase. OTOH, maybe rEFIt could activate the BIOS mode if you put the UEFI DUET software on a different partition from the EFI System Partition.
If you want to try, I recommend installing the UEFI DUET software to an MBR USB flash drive. That might activate the Mac's BIOS support mode and enable the software to run correctly. If it does, you can experiment with installing Windows to a GPT disk (still using the flash drive to start up the UEFI DUET software) and then see if you can get the BIOS emulation to activate using just your normal GPT hard disk. If you can get UEFI DUET booting with the USB flash drive, it's likely you'll be able to get Windows installed on a pure GPT disk, but it's conceivable you'll be chained to the USB flash drive to boot Windows.
I'd like to emphasize, though, that this is very "bleeding-edge" stuff. You're as likely to trash your data as you are to get a working system out of it. Therefore, you should proceed only after you make complete backups and only if you fully understand and accept the risks.
