Don't tell the kid you're going to Edm - that will only make it worse
Seriously though, 1 hour intervals seems pretty short based on my experience/that of my friends. Edm should be realistic with one bathroom break. Really though, it's not the kind of thing that is going to be fixed in one trip, nor will the process be easy/relaxing. It sounds like now might not be the best time to tackle that problem (although it really should be addressed soon). Keeping the kid distracted/engaged in something else is probably the key. Perhaps have the mom sit in the backseat with the little guy and try to engage him in games etc...lots of options here.Try to make it to Red Deer, then break for an activity (something fun/active for him) and then push on again.
Good luck!