Eh, it's fine, turned out my hometown went ahead with that municipal fireworks display after all. Forgot all about this thread after that until now.
Another question, for future reference; would glass store the hydrogen more effectively? If so, and if I put a balloon full of air over the tip of the bottle, would it become 50% hydrogen by diffusion? (Or alternatively, more than that because hydrogen is lighter than air?)
And even if so, would there be a way to get the concentration higher than 50%? Would a tube of water inserted underneath the balloon, filling the bottle, force hydrogen into an empty balloon wrapped over the tip?