The actor previously assisted Sanjay Leela Bhansali in the making of Black, a film about a blind and deaf girl's friendship with her tutor who suffers from Alzheimer's.
Mid Day reports that Kapoor will begin filming the extra as soon as the film itself starts shooting next week.
He will also be responsible for editing the feature, which will showcase his co-stars Priyanka Chopra and Ileana D'Cruz.
In the film itself, Kapoor will be playing a comic character modelled on Charlie Chaplin and Mr Bean.
Barfee director Anurag Basu is said to be keen on Kapoor making the short film.
A source told the site: "He's going to have fun with both Priyanka and Ileana since they know him for his pranks. They jokingly complained that Ranbir would definitely pull some stunt on them."
Kapoor, whose breakout hit was Wake Up, Sid, has previously described himself as "very ambitious" with "his eyes fixed on his own targets".