First of all, let me say I've had IBS for 15 years. Only when I started the Bentonite and psyllium husk cleanse have I felt any relief and been able to "plan" an outing at a restaurant, etc., without worrying about having to cancel at the last minute!
I know what you are saying about needing relief urgently. I took Bentylol when the cramps and attack just wouldn't go away. I would be in the bathroom for so long and and the Bentylol helped with the pain. It did NOT stop me from having a bowel movement (I use that term loosely!) but it helped with terrible cramps.
Last year, my attacks got so bad, I was afraid to go to work. My doctor put me in Dicetel, which I took three times per day. This helped the spasms as well, only I had to take it every day regardless of how I felt for it to be effective.
Since I started the b & p shakes, it has REALLY calmed down my tummy and I have several bowel movements per day. I can't be on the cleanse forever (It's been about 3 months) so I now take only one shake a day and will taper off.
So, for emergency use and as little medication as possible, try the Bentylol. I know the goal is to not take any medications, but I think in some cases the benefits are worth it, especially in an emergency.