Sense this topic has re-opened i will submit an answer.
For custom frame lighting i believe it would be easiest to adapt a product that is already intended for use on bicycle frames or wheels such as what it seen below. It is a weather proof battery box wired to a silicone tube filled with chip LEDs, basically a rope light, the idea is the battery box attached to the hub, and the rope portion is woven through the spoke and centrifugal force with a little help from zip ties keeps it in place.
They come in a variety of colors from a variety of manufacturers. Thus is why i think this would be the most simple and cost effective form to adapt. You could simple attach the battery box beneath the stem or any area out of the way and zip tie the rope where ever you want it on the frame. you could combine colors and get creative with it quite easily.
I know that the US distributor J&B sells them so most bike shops in the US should be able to get them, and ive seen them other places on the net as well. Their rather popular for customizing cruisers.
Heres a couple images of them installed: