Okay, i try to summarise the steps i did on my system. Please keep in mind, depending on your system, some steps might be different.
Creating the installer
FYI: First we need to create our install medium. I don't know why, but using the createinstallmedia tool from apple didn't worked for me. So i had to do it the old way. In order to create a bootable flash drive, you will need: - Minimum 8GB USB drive formatted with Mac OS X Extended, Journaled partition. - OS X Yosemite Installation.app downloaded from the Mac App Store.
Use Disk Utility to format your USB flash drive as a Mac OS Extended (Journaled) using a GUID partition table. Find the file named InstallESD.dmg within the Yosemite installer app by right-clicking (or Control+click) and choose Show Package Contents. Go to Contents - SharedSupport and double click and mount this disk image. (The dmg file might be hidden) You need to mount another file within InstallESD.dmg, and this file is named *BaseSystem.dmg”. Make sure your USB flash drive is mounted, and in Disk Utility, select BaseSystem.dmg (not OS X Base System) in Disk Utility’s sidebar, and then click the Restore tab in the right pane. Drag the USB flash drive name into the Destination box in the right pane. Then click the Restore button and a bootable OS X Yosemite base system will be created. If prompted, enter an Administrator user name and password. Open the destination USB flash drive and navigate to the System folder, and then open the Installation folder. You’ll see an alias named Packages. Delete that alias. Open the mounted OS X Install ESD volume, and you’ll see a folder named Packages. Drag that folder into the Installation folder on your destination drive (where the alias was). The folder is about 5GB in size, so the copy will take a while, especially if you’re copying to a slow flash drive. Source for this HowTo. One last step, i had to do, was new for me. Open up the OS X Install ESD volume and copy over the BaseSystem.dmg and the BaseSystem.chunklist to the root of your installer.
Installing a boot loader to the installer
FYI: I used clover in revision 2953 in my case. If there is a newer version out there, you might want to use that one. Double click the Install Clover 2k r2953.pkg and click continue Important: Do NOT click Install as it points to your current macintosh hd. Instead click on Change install location and choose your usb flash drive. Now click Customize and choose the following settings - Install for UEFI booting only - Install Clover in the ESP Under Drivers64UEFI choose - CsmVideoDxe-64 - OsxAptioFixDrv-64
Now click Install
Copy over FakeSMC.kext
I had to due two last steps to get the Yosemite installer to boot. I needed to copy over a FakeSMC to the EFI partition of my usb installer and had to configure the Clover config file. Otherwise i was not able to boot from it.
If it is not already done, we need to mount the clover efi partition from our usb drive. To keep things simple, i downloaded the Clover Configurator tool. Click on Mount EFI - Mount EFI partition and choose your usb drive on the list of drives. Don't close the tool as we will need it in a second. See config.png
Open the mounted partition within finder and navigate to EFI - CLOVER - kexts
Within this folder, you need to create a new folder and name it 10.10
Open up the folder and copy your FakeSMC.kext into it. Optional: At this step i also copied the RealtekR1000sl.kext to get my ethernet to work. See kexts.png
Go back to the Clover Configurator and load in the config file from the efi partition Under Acpi uncheck all Fixes acpi.png
Under Boot check kext-dev-mode=1 boot.png
Under Graphics configure your graphics card For example: I have a nVidia 560 so i unchecked "Inject Intel" and instead checked "Inject NVidia" and "Patch VBios" Those settings depend on your graphics card and might be different! graphics.png
Save the configuration.
With these steps i finally was able to boot from my usb drive and install yosemite on my system. After the installation is complete, use your usb drive to boot into your new yosemite installation. Redo the steps to install clover onto your hard drive and configure it with Clover Configurator.
Once again, this are the steps which worked for me and my system. Things could be different for your personal system. If some steps are unclear, feel free to ask and i try my best to explain it.
Acutally i think that there aren't any benefits of the UEFI bios instead the legacy one. But in my case, i didn't find any method getting the installer (regardless if using clover or chameleon) to boot with the F12 bios.