Wow, didn't know there was a blind there at all, you've made my day with this hack!! Thank you!
I had a little trouble pulling the blind out (for it's inaugural appearance) because there is an electrical wire at the top fouling it in the upper track. I kept shoving the wire up & out of the way and the blind moved across .
There was a bit of pushing & tugging so I hope it hasn't damaged anything to do with the electrics.
I'm leaving it shut and won't need a cereal box to do its job!