I was thinking about using a large paper clip to hold the tubes together.
Fold the tubes on top of each other.
Push through the centre of the paper clip.
Slide the clip down the tubes to create a gap at the bend.
Slide the fixing bracket between the gap in the tubes, and secure to the fixing bracket.
(Or just neatly tape the tubes together)
Don't forget, make sure you fix the centre bracket in exactly the same place as on my diagram, or else the tubes will either be too long and hang very loosely or be too tight and jam.