Of course Apple doesn't officially support such efforts which is why communities have sprung up to help fill this gap. After all, without Apple's official support the process isn't quite a walk in the walk in the park that you'd expect.
Our favorite community to support such efforts in making what they call "CustoMacs" is TonyMacx86. Recently they published a guide on how to run MacOSX Yosemite on a GIGABYTE BRIX-s. You can check the guide out there but be warned: it's not exactly for beginners but anyone that's comfortable tweaking some settings in their BIOS should be able to pull it off.
So, are you reading to build a BRIXintosh?