I agree with others that the training starts with lots of teasing and then a "cum for me now" when success is very certain. To get to the point that 'cum for me now' will work anytime, it takes a lot of positive reinforcement, by setting up the situation for success, but slowly reducing the physical stimulation required to achieve it.
Regardless of personal tastes, this is one exercise that will not be taught with negative reinforcement = as in, punishment for not cumming. Each time during the training, the 'cum for me now' should only be issued when there is a high chance of success, and a 'failure' should quickly be minimised as just practise to a goal, and not a failure at all.
There will always be a mental block ("this will never happen with me"), and it is removing that block that is the key to success.
Small things like: "mmhhh you are already wet and I haven't even touched you" reinforce that arousal doesn't need physical contact. If a person can get wet from words alone, it isn't a quantum leap to get even hornier from more words and thus, not a big leap to eventually cum just from words.
Small steps like this reinforce in the mind that its possible and remove the mental block - and it will happen. How long that takes will vary with every individual. It may be days, weeks, months or even years, but it will happen if there is a patience and a positive attitude. And lets face it - there is lots of fun along the way, so the end goal is not urgent.
Someone here mentioned replacing 'cum for me now' with a trigger word like 'watermelon'. This can be fun for some, but I prefer to stay with the standard phrase because its so much easier to then introduce variations.
For example, phrases like:
Watermelon Now! (ok, that would work...)
but, it will be tuffer to:
"have lots of watermelons now"
"have a small watermelon now"
"have a big watermelon now"
"STOP that watermelom"
Anyway, fantassy4u has agreed to try this with me. She has agreed to report back here as we achieve milestones along the way (assuming that others are interested to hear) - but regardless of the success we have, we will have lots of fun along the way - and to me, that is the whole point.
Brosco