I managed to find a retail solution that is readily available on Amazon: the tomato arm cage support. The structure below still works, is custom tailored to any need, but the tomato arm cages are more flexible in purpose with a smaller footprint when not in use. Couple these tomato arm cage supports with 11mm plant stakes, the green painted, metal stakes that can come in super long lengths, and you have a fantastic custom cage setup for your tomatoes. You can configure this setup with 3 stakes, 4 stakes, or more to expand internal size. There are even arms with multiple brackets per arm so you can add more stakes or make the internal area much narrower. The arms can be irregularly positioned to customize plant growth as it happens. There are also some adjustable width tomato cage arms, but I have not tested those out.