This summer I did a bunch of dives in a short period. Overall, as my air consumption decreased & bottom time increased -- my bladder pressure also increased to the point of painful. Often I'd miss beauty of the last 10 minutes because of the nagging in my bladder but try as I might I could not pee underwater.
It seemed I was always the only one on the boat after the dive to pull down my wetsuit and rush overboard clinging to the stairs and peeing in what little bit of privacy I could find. Often it even took effort to pee in this public space.
One day the bladder pain went from bad to intolerable. In-between fantasies of surfacing, logic prevailed - what was the psychological block that was ruining my dang dive?
Luckily I was swimming just above a sandy bottom and others were busy with muck diving. Shyly, I found a comfortable position and kneeled on the sand allowing muscles to completely relax and closing my eyes, my mind envisioned a toilet, warm water trickling, a slow drip waterfall, peeing at the side of the boat - anything to take my mind away from SCUBA and peeing in a wet suit so that I could actually pee and relieve the bladder pain.
I must have looked very funny, but finally a little came out, then more and finally more. It felt very strange to literally pee on myself, but certainly the bladder pain subsided and as a bonus I was a little warmer ;-).
After getting over the initial psychological pee block - peeing underwater is easy and certainly more pleasant than a painful bladder (although in the beginning it does help to sit on the bottom, hang on to a rope or do anything to distract you from the scuba environment). Ok after a few dives I was over the crutches too.
But Ill confess, before I pee in my wet suit, I still make sure there are at least 5-10 minutes left in the dive so it rinses clean before the dive ends and I am left with a stench.
Good luck!