The most productive thing is to quit. Anyone who, in 2014, is still not paying interns is most likely not someone who can teach you anything. There is still plenty of time to find another internship for the summer.
That basic learning is takes place in the first days/weeks of anyone's new job. There is no basis that the employer should not pay him just for not knowing how to 'hit the ground running'.
He would be much better off taking the time to look for other opportunities.