I can sympathize. I've only ever had two occasions where I had a bit of an accident, with nothing showing, luckily, but I often have the urgent need to go. I have gone a few times in the woods along trails - not fun.
I used to get up really early to run and that way I think my intestines were still asleep until I got home.
Now I run a bit later (to work) so I get up early, have coffee and a big glass of water and usually relax at the computer for a half hour (like I am doing now :-)). If this doesn't work I know where the public toilets are along the way.
Get up earlier than usual, eat something, drink water and coffee/tea and relax, that's my suggestion. I hope you have a phenomenal run tomorrow!