Neat idea Lello.
It will be interesting to see the effect when you achieve when you get into your studio.
I do not have a similar tube to try this out at the moment. My initial thought would be to have a square mount frame so that an adjustable reflector could be added on each side to make a bit more of the lost light.
Me playing with lighting thats not flash based - now that would be a first.
No idea of the subject distance on the attatched pics to get a feel for the exposure required.
Don