If GRUB 2 is installed to the MBR of the hard disk, then that implies that you're booting GRUB 2 in BIOS mode. A BIOS-mode GRUB cannot boot an EFI-mode boot loader. Thus, if I'm understanding your situation correctly, what you want to do is not possible. That said, there likely is a way to accomplish your ultimate goal, whatever that is; however, the path to achieve that goal depends on precisely what the goal is and what your current setup is, and you've provided insufficient information about both of those points. I recommend you begin by running the Boot Info Script and posting a link to the
RESULTS.txt file that it produces. This will provide us with detailed information about your current configuration. In addition, please describe in words what you want to achieve -- for instance, you've got a working configuration of OS A and you want to install OS B; or you're moving a hard disk from one computer to another and you want to get the OS on that moved disk to boot on its new home computer. Please edit your original question and add a comment to this reply so that I'll be notified of the new information.