Everything I have been able to find reinforces my memory that contributions are limited to the amount of Self Employment Income. 

You say he has some SE income from a partnership? Does he have an SE loss somewhere else that is offsetting the partnership SE income.?  Also if he has a Schedule C that is the SIMPLE sponsor, I do not know if you can count the K-1 SE income in computing his allowable contribution.

BTW @qbteachmt Simple Contributions ARE NOT by paycheck deduction for the owner of a Schedule C business or a Schedule F farmer, as the owners do not receive paychecks, nor would contributions  by partners in a partnership which has set up a SIMPLE plan.