Obese anglefish wants to interact with me. What should I do?

I inherited a filthy 40gal tank with a 3.5yr old obese freshwater angelfish named Sweet Boy. It was a rush job, so the newly cleaned tank is cycling with Sweet Boy in it. All water parameters are currently under control. I can't add tank mates for at least 30 days.

Here's the rub. Sweet Boy is my first fish. I have a lovely lively shrimp tank, my first and until recently only tank. Sweet Boy obviously wants to interact. He watches all of us, gets close when we peer into his tank. I want to teach him tricks and play with him, but I don't know where to start. I can't use food as a reward until he slims down.

Any suggestions welcome.