Again this is hot, take him right to the edge then threaten him to not cum, be as aggressive as you can muster, as you keep stroking him:
‘Don’t you dare cum, if you cum I’m locking you up for a month’
‘Don’t you fucking cum, you hear me?’
‘If you cum I’m going to make you eat it’
ironically those probably make him more likely to cum but it’s fun to watch him struggle.