I would suggest a different approach. When there is a region, by definition point must be at the beginning or end of the region. Which means you can simple enter the text you want at the beginning (or end) of the region. C-x C-x will move point to the other end, where you can enter the second half of your wrapper.
You don't get explicitly asked prompted for the insertion text, but I can't imagine there would be a way to accomplish the same thing with less effort.