Keep the money for yourself, and spend 100 hours of your time talking to a poor person. Help them find a better job, or make a better financial plan, or eat healthier, or just listen to what they have to say and tell them they can call you if they need someone.
This is by far the biggest impact a person like Paul Buchheit could make on the world. Even if his $20k could go 100% to a better water bottle in Africa, or a more efficient hybrid, or whatever, it will pale in comparison to how he could personally change someone's life if he walked up to them and took the time to try.
So go blow $20k at the club or on a cool car, after you've earned it by hitting the streets and solving your neighbor's problems for 100 hours. Someday your neighbors might do the same ;)