summer internship - getting work from other departments?

I'm currently doing a summer internship as a trading intern. given it's for trading, there isn't much for me to do to help the team, other than doing news runs, doing basic number punching, etc etc. on the other hand, I've been asked by two other divisions, both sales, to help them out with the work. particularly, for one of them i was directly asked by the director, who's my mentor, if i can help them out on a regular basis. after hearing this, my boss told me that while helping them out with a task here and there when they're busy is fine, but that i should use the time i have at the firm to learn more about trading. i understand where my boss is coming from, but i feel like there's only so much to learn when it's just me reading the news and research reports, and given i spend maybe 10 hours a day doing that, i would really like to get some other type of work, especially since i'm also very interested in sales. How should i get around telling my boss this is what i want to do? Also, i was hoping that doing work for the other divisions would also help me get a chance at getting an offer from diff. divisions, but i'm worried that this will just piss off my boss and lower my chances at either divisions.