I was tinkering around (surprise!) and stumbled upon a low-cost, fairly decent method to prevent pullouts.
Once I had the base ring on for my A271 device, I added two metal rings that sit over just the glans without covering the shaft. Then I attached the cage part and locked it down. This bunches up some of the shaft skin (I’m circumcised) behind those rings, while the glans acts as a seal at the other end. Attempting to pull out with these rings in place causes the shaft skin to catch against the cage, which is pretty painful if you ask me. Even removing the cage can trigger this binding effect, so care is needed when unlocking. On top of that, it seems to keep my penis pressed firmly against the back wall of the cage—a nice little tease during waking hours for me; some folks might find it a bit much.
I’m not entirely sure how well this setup holds up 24/7, but it performs excellently for daytime wear (I head out at night when she wants to play).