I don't think the bladder thing is as easy to "overcome" as a phobia like arachnophobia.
I have arachnophobia... and I can kill a spider. I can probably even force myself to enter a spider-filled room for something important...
But the fear does not go away. I'm still scared of the (*)(*)(*)(*) things.

The problem with this particular bladder problem is that the response to the fear is the lock-up of a bodily function that isn't normally controlled in as conscious a manner as, say, walking into a room. Remember, it's relaxation that releases waste... not action, as like running into a room full of spiders.
When you are afraid you may be able to make yourself run or fight... but relax? Doubtful.

__________________
"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside