1. Download this boot.efi file. This file has been patched to allow basically all capable-but-restricted-by-Apple Macbooks to boot into 64-bit kernel in Snow Leopard. In my case, this enables my Macbook5,2 to do so.
2. From where you saved this file, in terminal, do this:
sudo cp /System/Library/CoreServices/boot.efi ~/Desktop
(this step saves a copy of your original boot.efi to your desktop; unfortunately I lost mine!)
sudo rm /System/Library/CoreServices/boot.efi
NOTE! I did not test this and this is irreversible. Please make sure you made a copy of this file. If you cannot delete it this way, do it in Finder.
sudo cp boot.efi /System/Library/CoreServices/
Copy the patched file to where it should be.
3. cd /System/Library/CoreServices/
4. sudo chown root:wheel boot.efi
This changes the ownership of this file.
5. sudo chflags uchg boot.efi
This locks the file.
6. sudo bless –folder /System/Library/CoreServices/ –file /System/Library/CoreServices/boot.efi
7. One last thing is to add arch=x86_64 to file /Library/Preferences/SystemConfiguration/com.apple.Boot.plist to Kernels Flags section
You should be done by now. You may still need to hold “6” and “4” keys when booting. But it should work.
How to hack the boot.efi file comes from here. Basically Apple restricted all non-pro machines from doing so with this file. So that’s why we need to change it. What changed was:
38 47 01 00 00 00 00 00 00 00 00 00 00 00 00 00
38 47 01 00 00 00 00 00 04 00 00 00 00 00 00 00
Additional resources from here.