Capra Audio was the one I was thinking of - I believe all their straps are 3D printed and tailored for their headphones at the moment, but the underlying principle of how they’re attached is the same throughout. Might be worth checking out and taking a bit of inspiration from. You can even download the 3D printing files and fiddle with it. https://capraaudio.com/
The other alternative is looking to see if there’s anything on like Aliexpress that could help. Look for something like “headband replacement”.