This was a technique I developed to wank undiscovered in a four bedded hotel room I occupied with my wife and two kids. Having the kids in the room meant no marital fun and one week was more than I could go without some kind of release.
My technique involved laying on my right side in my single bed and using my little finger on my right hand. Once my cock was hard I hooked my little fingernail into my frenulum (the little bit of skin between the cockhead and the foreskin) and teased it gently with very little movement. I could keep this up for quite a long time with some intense fantasising.
When I finally came it felt like a knotted string was being pulled out of my cock - in a very good way. I spurted about half a dozen times - more than usual and the feeling was more intense and satisfying than normal.
And yes I did tip the maid !