Hey Rab,
The only problem with using painkillers for IBS on a regular basis is that they tend to mess with the gastrointestinal system, causing constipation or diarrhea, which can make your IBS worse. However, I've had to go to the ER probably about 6 times over the past two years for treatment of my worst symptoms, and have received either IV morphine or Vicodin for the pain. Those certainly took the edge off until the symptoms passed (usually took a few hours), but I would be VERY careful with how you take them, as you can easily become dependent on such drugs and that would be no fun at all. It might be best to see a pain management doc if you can get a referral; that way, they can monitor your usage.