You flip through the spellbook before finding one near the end that the nerd apparently hadn't investigated in detail yet.
"Another Man's Child," you read from the book. "Huh, looks like this'll be fun. Swaps genitals with the target, allowing you to impregnate people using others' seed, piss out of either bladder, and share, transmit, or deny pleasure and pain all by yourself. Curse breaks on taking a solid hit to the taint instead of the genitals proper, one good kick or a few punches should do it."
You read through the fine print below, and grin. "You're gonna have to respect the meat, or I don't respect yours."
Tap circle, aim, fire.
It's a boring 'poof' transformation where suddenly your pants feel a lot less stuffed and the nerd's robes are tenting. While the nerd makes some gibbering noise at suddenly having decent-sized junk, you pull your pants open to reveal...a micropenis and mini-balls to match. Slightly paler, circumcized, not much hair, and underwhelming enough you wondered how old this guy was. Cradling them amicably between a few fingers, you pinch and prompt a soft yelp from the nerd who'd already started feeling up your junk that you'd so gracefully equipped to him, a sensation you shared in fully.
"Alright, fucko." you tell the nerd. "I'm in charge of our dicks now. That's my cock you're handling, so unless you want me pissing your pants or showing you remote CBT, you treat it right. Jerk it off when I tell you to and maybe I'll let you feel it so you know how you're doing. You got some way to hide, but clearly it doesn't work on everything since I caught you. How's it work?"
"I masturbate and it makes people I don't exempt not care what I do while I'm doing that." the nerd said. "It's based on a diagram I internalized, it'll work with your cock attached to me too. If I exempt you, you can communicate with me and I can communicate with you, and nobody will think about talking to the air or anything."
You have an idea.
"If I used the submission spell on you, would you submit?" you say deviously.
"Y-yeah." the nerd stammers, somehow this being the breaking point of embarrassment. "I'd love to!"
You flip to 210, tap, and blast him into compliance without a second thought.
"Alright nerdy birdie," you say to your newly christened submissive as you haul him down from the coat hooks. "Don't resist me, do what I say. What's your name again?"
"Dexter John Gwilym." he answered.
A few short questions about contact info stuffed in your phone for later and properly securing the book of curses, you still had to piss. There were plenty of good toilet stalls right there, but there was a submission spell to test. Ugly thing probably wouldn't be good for blowjobs yet, but as a urinal...
"Alright, on your knees, suck it." you said to Dexter, gesturing to your borrowed boyhood. "I'm going to piss, and you're going to swallow. Enjoy it, that's an order."
Shoving his cocklet into his face, you finally dealt with your need to piss, and his too while you were at it. The indescribable sensation of getting a boner with your real bushy eight-and-a-half inches while it wasn't on you was distinct from personal arousal, while Dexter's order to enjoy was interpreted sexually providing unusual watersports backdrop anyway. Both bladders channeled out one dick for now, you gently pulled Dexter off and ordered him to help you with your next plot: messing with the boys by having a fat nerd shove your cock in things before the game. He'd exempt you from his masturbatory undetectedness, and you'd tell him what to fuck around doing while constantly jerking you off. Even if your dick came, you'd just order him to keep masturbating until him showing up wouldn't be an issue and delight in the filtered overstimulation.