About the only thought that occurs to me to improve this would be to use a thick enough chunk of plexiglass that you could drill into the side of it and then glue-gun the LED's in place, then you can run the wires across the top edge of the plexiglass sheet off to either the top right or left and then move off from there. This would allow the duct tape to be removed and still have everything stay approximately in place. As a simpler idea, I'd recommend using a single piece of long black electrical tape to hold it together. It would look more professional.
Another idea would be to put one blue LED (and swap out the red one there) in the center LED position - this should make an interesting shade of purple. Or just use blue LED's instead of the red.
Nice thinking on using the USB port.
Interesting project. Thanks for the post.