Here are some V-Sit exercises that you can do on a BOSU-ball. The first one is just very basic, where you would sit in a V-Sit. Right here, your butt is in the middle of the BOSU-ball, hands back so that you have some support. You can put them on the floor as well. You're going to bring your legs up into a V, and you can keep holding on if you need to, in order to stay balanced. If you want to try a more advanced version, then you have to come a little bit forward on the BOSU-ball. Bring your legs up and then you bring your arms out to the side and hold it.
You can also bring them up here, which is even harder. Another thing you can do in a V-Sit is, you can take a dumbbell and you can hold it out both legs. You probably want to keep them bent, and then just take it from side to side. One more thing you can do in a V-Sit is, you can actually bring the V into a close, and then back out, which works your abs. Again, hands back here. You would just bring it in and then right back out, in, right back out. You will definitely feel this in your lower abdominal's. These are different kinds of exercises you can do, all for your abdominal's in a V-Sit.