This same thing just happened to me! I never used Immodium for the same reason you stated. But I just started a long commuting thing two days a week. On my first day of commuting, I was hit with an attack of D about halfway there. Had to stop, but then I went ahead and took some Immodium. Felt much better the rest of the day, but have had C ever since (diet has made no difference). The C made the second day of commuting easier, but I don't like these extremes.
I don't think it's good for day to day maintenance, but it definitely works in the short term if you're traveling. I'm interested to know if anyone has methods of getting things going again once you take the Immodium.