I was able to do this when I first got my rmbp - unfortunately it bluescreens on the 2nd boot of the setup process. I wasn't able to progress or work through it so I went back to traditional boot camp. I realized that AHCI is now natively enabled by apple, which was my main reason for wanting to efi boot (to get trim working so as not to harm SSD performance over time) so I haven't revisited efi boot...