Mmmm. Long story or short answer, that is the question??
I have had the desire to experience incontinence since I was about 11-12, but it was only after I got private medical insurance through my job much later in life that I was able to make any progress towards getting professional help.
I started by seeing a Harley Street psychiatrist who was very supportive, and not only wrote to my GP, but also referred me to a Urolologist friend of his. Although his friend was not able to help, he in turn referred me to another Urolologist. It was this doctor who after 2-3 years of discussions eventually agreed to do the first Botox injection as a supplement to a bladder neck incision that I needed to cure some genuine urological problems that I had at the time. He also did the other two Botox injections without hesitation when I requested them.
As I said previously the closest I got to being incontinent, was after the third try, when I had the bladder control of a potty training toddler, and would eventually end up wetting my nappy; not quite a flood, but a good stream.
I was upfront and completely honest with the psychiatrist, both urologists, and my GP about what, and why, I wanted as this was the only way that I could see to achieve what has been an almost lifelong desire.
Unfortunately Botox is not a long-term solution, as the effects only last for between 3-6 months, depending on which muscles it is injected into. The stronger the muscle, the quicker the effects will wear off. So, no I am not currently classed as incontinent.
If you could get a Urolologist to inject the external sphinicter with a long acting local anesthetic, you should get the 'benefit'? of the effects for about 6-12 hours.