Custom request:

Slave is in the cock-board.
You give him a shoejob in your boots until he cums. Then you rub the cum under your boots and onto his cock.
Once he his covered and lubed up, you jerk off his dick again until he cums under your boots a second time.
for the first cumshot, start off slow and soft, then when he's close to cumming do fast strokes. The same for the second cumshot, but this time jerk his cock between your boots so that when he cums, it sprays on the boots.