“Hey Coach, it’s my boyfriend’s birthday and I was hoping you could help me out with a gift for him.”
What did you have in mind, jock?
“I’ve always been a total top in the past, but my boyfriend is vers. He’s been so good about only bottoming with me, but I know he wishes he could still top sometimes too. Could you help me become comfortable with bottoming?
“Sure thing, jock. Let’s start by having you think of how much you already lust after your boyfriend. You obviously have an attraction with him, perhaps an attraction on multiple levels.
Focus on that attraction and allow yourself to feel that lust for him now. Think of how sexy he is to you. Think of all the things you already love doing with him. That’s it, I can already tell you are lusting after him hard, your dick getting harder and harder as you do. You can take it out at any time you’d like and really let it grow as you continue to fill with that growing lust. 
As you continue to give in to both the pleasure of relaxation and the power of lust, realize how hard you have become at the thought of pleasing your boyfriend. He is someone you yearn to make happy, and it feels good to do whatever it takes to please him. This in turn pleases you, always so pleased when yo have pleased him as his pleasure becomes your pleasure. This becomes true for all times, but you especially love to show him how special he is to you on those special occasions like birthdays.
As you continue to give in to both the pleasure of relaxation and the power of lust, realize how hard you have become at the thought of pleasing your boyfriend. He is someone you yearn to make happy, and it feels good to do whatever it takes to please him. This in turn pleases you, always so pleased when yo have pleased him as his pleasure becomes your pleasure. This becomes true for all times, but you especially love to show him how special he is to you on those special occasions like birthdays.