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.
So the best strategy is to sit down with the boss and outline a plan that either a) clearly explains the things that your friend is going to learn during this internship (and it is an internship) and a timeline for learning them.
That's a lie, actually; the best strategy is for your friend to find somebody who's willing to pay him money for services rendered. But assuming for some terrible reason he absolutely has to stay with this startup, then he should figure out what he's going to get from it and the timeline for said getting.
See this for more: http://www.bothsidesofthetable.com/2009/11/04/is-it-time-for...