you know, you are right - color me embarrassed...
i was sure that i had seen a single row of leds like dreamworks used to sell, installed between the inner and outer pipe, but maybe not. I know that the double ringed ones are too wide to go in there. There's at least a 1/4" between the walls on the mueller pipe in my panther and it seems like that could work - if the ring was the right size, but on my other pipes, there's not enough room...
My bad...
bob