Invest the money with non-zero interest, return the original money, and use the extra to... realistically, pay the salary of the person who did the investing.
Yeah, if I had a non-profit, I would just plainly refuse.
I doubt someone who wants a pet foundation to succeed would ask for repayment unless they really dropped the ball. Of course, this assumes the person doesn’t anticipate needing the money, which in the case of the WhatsApp co-founder is true.
