I suffer from the same problem. It requires me to run near my house or work for at least the first two miles of every run (I do a lot of running around the block). If I can either make it to the two mile mark or until after I stop for a bathroom break, I’m fine to run as far and as fast as my body will take me.
I know some people take Immodium to help with this problem, but I don’t want to put myself in the position that I have to take it everyday. I’ll be interested to see if anyone has some helpful suggestions.