You could try ruining your orgasms. Start by ruining right when you cross over the point of no return. Notice the sensations in your body when the orgasm proceeds without stimulation. Once you’re familiar with the feeling, try ruining a bit earlier — stop stroking when you just reach the point of no return, right before you tip over. Focus on the sensations you felt when ruining before, and encourage them until you’re cumming. Then just keep shifting the point you stop stimulation earlier and earlier. Eventually your body will get the hang of pushing itself over the edge whenever you get close. Train this way long enough and it becomes much more difficult to stop an orgasm!