So, you're a teacher who's discovered that Khan Academy is more than just Math! Totally awesome, right?! But how do you sign up your class and make recommendations?
There is a wonderful guide on the site with recommendations for teachers in non-Math classes. The short story, at this time a teacher can use the material, but, since the only Missions are for Math and Computer Programming, you will have to resort to old-school methods for assigning topics.
You can still set up a class and use Khan Academy to monitor if the students are actually watching the videos and (where available) doing the practice questions you assign. On the Student progress report for a class you can click on a student and then click on Videos to see what Videos he/she has watched, or click on Focus to see what skills he/she has worked on (including those skills outside Missions). You will just need to give the assignments in the same manner that you give textbook assignments to your class, whether that is verbally, a list on the board, a printed list or even an email message sent to students/parents.
Note: The class will appear as a World of Math class. The students are not required to work on any math material.