The real question is, how far you want to go and what's the risk?
My girlfriend wanted to mess her diaper while sleeping and wake up in the morning with a full load in the diaper. For her it was important, that she sleeps until the morning and that she doesn't wake up while messing the diaper.
So as she is a physician (ok, she is working in research and not with patients, but she knows how to do it) it wasn't very difficult:
She took about two hours before bedtime 30g of magnesium sulphate in 200ml water. Because I knew what was coming, I diapered her very well (thick night diaper and plastic pants). Around bedtime she felt that the magnesium sulphate started to work. So she took a 15mg midazolam (to fall asleep) and a 10mg diazepam (to stay asleep) pill.
After about 20min the medication kicked in. Some minutes later she was still awake, but very sedated, when she started to relieve herself into the diaper. Only five minutes later she was asleep.
She woke up late in the morning and of course couldn't remember messing her diaper, even she was still awake when it happened. Midazolam very often produces amnesia (in this dosage in about 80% of all patients).
Over the last three years, we did this about five times and I strongly recommend not to do it more often.
KEEP IN MIND:
What we did is very dangerous! She is a physician, so she knows what the risks are, but most people don't! Dying from hypoxia is a real risk when taking high dosage benozdiazepines. As precaution I hooked her up to a pulse oximeter and I'm a trained paramedic (even when I'm not working in this profession any more) and of course I was absolutely sober while doing this.
P.S.: She once gave me the same treatment, but with iv midazolam, which works in seconds. So I could wait with the sedation until the laxative gave me extreme cramps (I took four Dulcolax two hours before the magnesium sulphate). She told me I was still awake, when I filled my diaper, but of course, when I woke up four hours later (she gave me no diazepam) I couldn't remember messing my diaper. This was the greatest thing that happened to me while wearing a diaper.