Assuming there is sufficient room in your cubicle/home office, I would suggest getting an appropriately sized Swiss ball to sit on. In general you'll be moving around slightly while on it, which will help stimulate your core stabilisation muscles. It's also quite easy to do a back bend over the ball, which would be a good idea to do throughout the day to compensate for being hunched forward (even on a ball, there will be a tendency to hunch over). Once you get the hang of it you can also try switching how you sit on the ball. I enjoyed sitting in lotus for 10-15 minutes at a time while on the computer, and kneeling on the ball could also offer up a change, although I found that to be harder to sustain.
If you can get the time to go to a weight room once per week that would also help, doing exercises like deadlifts, squats, presses, dips and pull-ups will put your body under a heavier load than it's normally used to, and should help you be less susceptible to back and neck problems.