If you've tried all the tricks I've mentioned in the blog over the years; thrusting and squeezing the butt cheeks, direct prostate stimulation, change in location, sleeves, and cock rings, and there's still a failure to launch, I'm not sure I have an answer.
Our cocks go soft at varying rates after we cum. It sounds as if the brain is sending a signal (chemical in nature) that the ejaculation has happened. If there's a medical solution to that, I can't find one.
Maybe you should give your friend's suggestions a try. I mean, what do you have to lose? It either helps you cum or it doesn't. If it does, you get the physical (and mental) relief you need. If it doesn't, you aren't any worse off than if you keep trying alone.
I know some of my readers are in the medical field; perhaps they might offer ideas.