another option, maybe?
How about this: Instead of taking all the foam out, make up a "drill" out of 3/4" or 1" tubing, the end of which you have filed teeth. The tube could be a length of copper plumbing pipe... a ten foot length is only about $5 by me. Then you could twist this, while pushing, and pull it out occasionally to take out the bits. This should make a 1" hole through the foam, through which you could thread your wires. To make the necessary 20' length, solder two lengths together using a straight junction. It would not stick out too far, and is only about 65 cents. Rich.
