Being in two point without stirrups is absolutely possible, and a very very important exercize that builds up the muscles that allow us to have an independent seat. If you are having problems, then you are probably confused about which muscles control posting. You should post with your thighs and NOT with your feet, by standing up in your stirrups. Two point is similar to the higest point in the post, where the only points of contact on the horse are your thighs and your calves.
In posting, you should be letting the horses natural movement push you out of the saddle, and then you control your movement up, and your descent back down, with your inner thighs.