I managed to get my hands on a HERO 3 casing and produced a new version of the mount that is a bit longer and has a 40deg bend in it to suit. Same idea, just mounted further out.

On the bike. Fits the standard GoPro mount (would be pointing up at 45deg angle on my first design!) and clears the saddle bag.
EDIT: I've sent one of my spare Fizik/Cateye mounts to WheresWaldo so he can work his magic on it...