HACK - I attached my MAJGULL blackout curtains to my SANELA curtains using leftover RIKTIG wire curtain hooks. Way easier than everything that I was thinking of doing. It looks and works
IKEA MAJGULL Fabric 150 cm Room Darkening Light Grey/Beige : Amazon.de: Home & Kitchen
AiiikeA PAKA - IKEA MAJGULL Curtain Langsir Sliding Door Block-out curtains, 1 pair, 145x250 cm Curtains Ikea Ready Stock Size : W145 x L250cm (1 pair) Color : Dark Blue Material :