Plant the beans in the loo rolls, the roots will find their way out of the bottom, so you don't need to disturb the roots at all. Also, I find that by putting a bit of self-adhesive copper tape around the top of the loo roll, you will keep the slugs and snails at bay during the time that the plants are so vulnerable to attack, that is, when they're young and tender. And eventually the loo roll wil rot down and disappear. It's win-win!