[UPDATED 15 Mar 2013]
Apple has finally released the trackpad drivers for Windows 8! It's not as straightforward as I was hoping as the BootCamp 5 install fails but it's quite easy to get it working manually. If you download the bootcamp drivers (http://support.apple.com/kb/DL1638) you might run into an issue where it tells you that "Only Windows 7 can be installed" on your macbook or "x64 installation is not supported". Luckily, all you have to do is run the driver called AppleMultiTouchTrackPadInstaller64.exe and it will update the trackpad drivers for Bootcamp 4 if you have that installed.