Kim, you are very bad!
Barakta's got one (I can't remember what brand) on her ICE trike, to make it easier for her to reach. We've had a couple of unplanned bottle ejections though, so it might not count as lumpy track proof.There's a twist-entry version of the Monkii Cage that might work: https://www.cyclemiles.co.uk/shop/cycle-products/monkii-v-cage-bicycle-bottle-cage(I use the normal slide-downwards version to hold a standard 750ml bidon vertically on my Brompton stem, and can vouch for it holding securely.)
I've got both and I would not recommend the V cage as an alternative where a small frame restricts access. In fact you need slightly more space for the V version because you need to twist it and slide it. Finally, you can't really access a Monkii Cage (or a bottle in it) while riding. The plain Monkii Cage is great for carrying things of not-quite-water-bottle size, including larger bottles of water or fizzy pop but not as a bidon cage.