This is the best route, by far. Most importantly, it would involve a period of continuous diaper before irreversible changes - so you would have a chance to change your mind. A next step, if this wasn't working fast enough for you, might involve other non-invasive methods like more active retraining or hypnosis.
Of course, wearing 24/7 is irreversible in a way. Family, classmates, coworkers, etc. will become aware to some extent - and once they notice, will expect you to continue wearing them.
Not bad for 5 min of research. Technically, the conversion between wall stress and content pressure is s = pR/2t, where p is the pressure, R the bladder radius (if it can be approximated as spherical with a discrete wall), and t the wall thickness. Of course, there are a large number of unknowns. A pessimistic guess would be that the catheter balloon would be compressed from one end towards the other until the tensile stress due to tension and pressure caused it to burst. The inner sphincter would see a tensile stress. Since it handles tensile stresses all the time, this might not cause damage. The bladder/urethra lining would see a shear stress, and since it isn't used to seeing a shear stress, might be easily damaged. This would provide a route to infection. Conceivably, this, lack of medical attention (since he wouldn't want to admit to doing this), and some complications could take out the kidneys, etc.... while leaving the sphincter itself undamaged. Yes, among all the other bad outcomes, there is also a risk that the stunt might leave one dependent on dialysis but with full bladder control.