Give him a hand.

"Oh, fine..." Beth sighed. Something told her that playing annoyed and disinterested would work out well for her. "Show me your little problem, Seth. I'll see what can be done about it." she rolled her eyes, but made a point to rub her pussy openly.
"Oh, I'll show you...." Seth was all too eager to drop his trousers to his ankles. He reached into his waistband, pulling his cock free over top of the restricting elastic. It stood at attention, pinned to his body by the tight band, with the balls remaining concealed beneath his briefs.
"Hmm...." Beth put a finger to her lips. "Not bad." It wasn't bad. He was definitely at least equal to Brian. Don't think about Brian right now. Just give him a little fun and get out. "Alright...since I seemed to have caused you a little bother...." she slipped sensually from the desk, kneeling gracefully in front of him and taking his shaft in her hands. He grunted softly as she rubbed it with her fingers, running her thumb across the sensitive underside of his tip and smiling at him over top of it. Working some spit into her mouth, she drooled it onto his cock without breaking eye contact, and began stroking him with a purpose.
"Fu...uck..." Seth groaned. Beth pulled his waistband down to free his balls, rubbing them with a free hand.
"They feel pretty full, Seth. When's the last time you emptied them?"
"A...c-couple of days ago. I don't je-ERK off that much..."
"And no pretty little something to help you out?" Beth put her voice somewhere between sympathetic and patronizing. With his cock in her hands, Seth was in no position to object to her teasing.
"Not...for a while now..."
"Oh, that's...too....bad...." she punctuated her words with slow, tight-gripped strokes from head to base, rubbing his balls.
"Fuck, that's good..."
Beth worked harder and faster, occasionally hovering her open mouth tantalizingly close to his cock head before smiling, or sometimes just drooling more spit onto it. She could tell Seth was getting really frustrated, but whenever it seemed like he would pop, she slowed down, and relaxed her grip. "Oh...are you getting close... you want to cum, don't you? Maybe...in my mouth?" Beth made another feint, moving as if to put her mouth over his cock.
"I knew you were a tease, but..." Seth let looked upward, blowing his cheeks out in frustration.
"You're going to give me what I want...right?" She began stroking hard, and fast.
"Yes...!"
"Whatever I need to succeed?"
"YES!"
"Make me believe it, Seth...or I might just..." she slowed down dramatically, and a look of panic appeared on Seth's face.
"NO! I PROMISE! JUST DON'T STOP STROKING!!!"

Beth decided that she believed him, and she chose not to ruin his orgasm. She stroked vigorously as Seth shot stream after stream of sticky, hot whiteness over her hands. She laughed with delight, even catching one of the spurts on her lower lip by accident.
"Fuck....."
"Remember...." Beth admonished as she wiped her hands on a napkin from his desk. "...remember our deal, now."
"Y...yes....." Seth was out of breath, slumped in his chair. Edging him and then bringing him over had sapped his strength, and apparently it had made him pliable and receptive to her demands.
"You've got a nice cock, and you shoot a good load. I like that in a man." Slutty talk from a slut. Just get dressed and get out of here! She dressed, but slowly, making sure Seth enjoyed her movements. "I got to go, but I appreciate your help." She leaned over to give him a kiss on the lips before sauntering out of the office. It wasn't until she reached the car that her facade cracked. "What the fuuuuck...." she whispered to herself. Her fingers smelled of cum, and she was sweaty. Not to mention the tasty glob of white that she had licked from her lip. Well, that could have been worse, but you got what you needed, and for what? A little handjob? No big deal. She repeated that to herself as she drove home.