How to make a blackout lining for bamboo window blinds

Susan says:

I have bamboo roll up blinds on 2 windows. They are see through at night. How do I make a privacy cloth backing for them? Thank You.

Our decorative painting expert, Judy Leasure, has made some Roman Shades recently and this is her suggested solution:

I have made Roman shades and with those you sew your fabric and the lining together and then sew rings on the lining side. When the shade is finished, you thread cording through the rings and across the top to one side. To raise, you pull on the cords (which are all joined together so they pull uniformly). To lower, you release the cords. If the bamboo shades work the same way, you would have to find a way to create a channel around the cords so they will move once the backing is applied.

You might try making a liner of black-out fabric by cutting a piece of fabric 2 inches larger all around than the shades. Hem all 4 sides with a 1/2-inch double hem. (machine stitch). Then align the liner with the shade and hand stitch with a heavy thread vertically along the sides and vertically in one or two rows in the center. Your stitching would wrap around every other bamboo rod on the way up the shade. Whip stitch the bottom around one of the bamboo rods and you may need to do the top as well. In this way, the mechanism should still work and the fabric will stay in place with the shade.

This appears to be a lot of work, but I can't think of another way to keep the functionality of the shades. Again, I'm not 100% sure how the roll-up mechanism works.