This is one of those 'uncut only' techniques. It also requires that your foreskin still cover the glans during an erection.
Masturbate without drawing your foreskin back at all. Simply use as much play in the skin as you can without taking the 'downward plunge' and exposing your glans. With this technique, a rougher 'squeezing' method can be applied, and cumming 'covered' is a rather different and pleasant sensation.