I was considering either creating a wooden bracket like the one that you showed me and actually afixing to my wall, or using three wall brackets to hold it up - something like this:
The guys at GA told me I should just bite the bullet and hang the lights from the ceiling. I was looking at some of the metal fixtures they've got there, and I think a 3' long metal fixture would also be too heavy for a wooden bracket without some kind of reinforcement.