Jaw breaker😯😮😵

Long story short my parnters head is the biggest I've met.. It's way worse when he's fully hard!! It almost makes me not want to tease him because by the time I get ready to blow him I can barely get my mouth all the over his head! It's ridiculous but a struggle none the less! Even trying to jerk him is awkward because of this. Any advise on ways to give a good feeling without dislocating my jaw? I already tried using hands with it.