For those who don't want to make their own Bellows Bungee or who don't want to shell out 25 quid for shipping from the UK, there's now a version sold by Reimo. The company is German but they sell across all (or most) EU countries. I've seen them in France for 7,00 € plus 7,50 € shipping, here: https://tinyurl.com/y3nw48a8