if you google V star 1100 driver backrest you can find things like this:
EDIT: I just noticed that listing has no price, but there are several more like it.
It usually attaches to the screws/bolts for part of the passenger seat. Whether you will be able to keep the passenger seat with it is hit and miss.
I got one very similar for my 650 a few years back. I had to mangle the bracket to get the back rest where I wanted it. It was ok but not great. Having anything you can lean back into even a little gives you a more secure feeling that you wont slide off the back of the bike, and allows you to relax the muscles in the small of your back. The one I had, if I put all my weight on it, Im sure it would bend back flat.
I later put a trunk on my 650 (photos in my garage page
<= over there) With a bit of padding the trunk is a better drivers backrest.
I want to put one on Ursa (royal star naked), but have not found one I really like. Ursa has saddle bags with the wire loop mounts, I keep the mounts on the bike and put the bags on when I think I will need them. I would like to have a drivers backrest that attaches into more than 2 side by side bolts in the fender or under the seat, so if I do stress it with my weight it wont bend the fender out of shape.
I have seen a back rest on a 70's Honda 750/4 that attaches to side rails (where my saddle bag mounts attach). It can be slid back for a passenger back rest, or slid up for a drivers back rest, or anywhere in between. I have not seen one for V star bikes, but that would be ideal.
I think that having anything you can lean back into makes the bike far more comfortable, esp on longer rides. Whatever it takes to put one on your bike, it will be worth the cost or the time you spend fabricating it.