A better thing would be to get carbon fiber off ebay and run strands parallel to the tube, and then over-wrap those, using quality epoxy (not 5 minute, aircraft or boat grade). Fiberfix would probably work, but the limiting factor would be how well it adheres to the tubes.
Carbon Fiber Tow IM7 12K 50 Yard Spool | eBay
I think that the break would need to be outside of at least 2 diameters of the adjacent tube, or you are looking at having to work a patch around a junction which would be a whole other thing. Also, if there was any way to get a plug in there, and pour epoxy into a solid plug in the area of the damage, that would be very positive. So if the tube butted into the adjascent tube with a solid wall, you could just fill the tube form that point till it came over the damage. That would be particularly useful if the damage was really close to the end of the tube.