You do not want this to become a habit. One of my horses figured out she could dislodge a rider that way. The first time, it was when my son (age 8) was riding. He hopped off, no one was hurt. I thought it was a fluke thing. Next time, my daughter's friend (age 12) was riding, and the horse laid down (she didn't roll this time). The girl hopped off and I decided to fix the problem. I got on and rode like a sack of potatoes. I didn't steer, I wasn't balanced, and I let the horse wander around. She found a nice sandy spot and started sniffing. I took my feet out of the stirrups and waited. Sure enough, down she went. I instantly leapt onto her neck and tried to pin her down. She managed to get back up with me on her neck, and I wiggled back into the saddle (fyi, climbing over the horn was interesting). I continued riding, and she never tried that trick again. This strategy is very effective at breaking that habit, but I would only recommend an experienced rider try it.