Comment 27 for bug 1298894

For those willing to try to make their Mac with 64bits capabilities boot 64bit kernels natively there is this hack ** you will use it by your own risk **

http://netkas.org/?p=127

For those who don't know if their EFI is 32 or 64 bits:
you have to know your Mac's processor and its speed, than go to this site:

http://www.everymac.com/mac-answers/snow-leopard-mac-os-x-faq/mac-os-x-snow-leopard-64-bit-macs-64-bit-efi-boot-in-64-bit-mode.html

...

I have been able to boot to Ubuntu 14.04.3 64bit after I made modifications to rEFInd's configuration files (while logged in in the OSX) on a originally 32bit OSX by intalling rEFInd (witch automatically detects the 64bit) and then tweaking the refind.conf.

BUT it will NOT work to boot a USB !!!

So to all who may try it , I recomend getting Textwrangler for Mac ... I is easier to copy paste that way ... they have a compatibility page and will run on anything from 10.4 onwards.

1) Download rEFInd
2) unzip it
3) open Terminal and do a "sudo su"
4) go the unzipped folder
5) type "./refind-install"
6) reboot your Mac -- new rEFInd boot screen - choose Mac OSX
7) after boot open Terminal again - "sudo su" again
8) Go to rEFInd folder again type "./mountesp"
9) go to /Volumes/ESP//EFI/refind
10) edit the refind.conf file as below (copy paste should work if you installed TextWrangler above)
11) reboot with the 14.04.3 DVD in the MacBook 4,1

Let us know how it went!

Rogerio