I learned this trick many years ago. Getting your prostate tickled while being jacked off or a blowjob. I learned it from a friend who earned extra money by selling favors. She said that if a guy is having trouble cumming, she would slide a finger up a guys anus and tickle the prostate. Way back in those oriental massage days.
It is very enjoyable and it really does add to your orgasmic pleasure. Later I told my second wife about it and she would use it regularly. Of course I would always make sure I had just had a shower and made sure that I was clean too. Very important. Enjoy it