Chronic backpain sufferers know the damage an ill-timed sneeze can cause. The whole-body convulsion can set off pain where there was none before, or (more commonly) make bad pain so much worse.
Once you feel the urge to sneeze, it is almost impossible to stop it. The trick is to keep it from hurting.
First, fight the strong urge to inhale deeply. Second, try to exhale as much as you can (this will take some practice, as it's the exact opposite of your innate response). With less air in your chest, your sneezes will be much less convulsive - more like a strong cough, if anything. After 3-5 of these mini sneezes the urge will pass.
You'll look and sound weird doing this, but it's worth it - since perfecting this technique nearly all my sneezes have been pain free.