You should look for the user macegr here. He has worked with narrow PCBs for LED bars, and I saw a couple nice designs.
Yeah, I had posted them in here but later realized they weren't ideal because they face in only one direction, so I deleted the post. But I guess it would be possible to put them back to back, or use a 4 layer PCB. This is the current design (forgive the late-night silk screening):
These are 4 inches long, 1/2" LED spacing if you put the PCBs edge to edge or end to end. Still needs some work but I should have some prototypes soon.