Find a group of close friends and set up a donor directed account (on Schwab or elsewhere) that you all commit to donate to every year. In 20 years or so you have a very large fund that you can start giving away during your retirement years.
CrowdRise allows individuals to establish and fund specific philanthropic campaigns -- "kickstarter for philanthropy". http://ti.me/RcHgdm
Matthew Yglesias argues that donating money to Harvard makes about as much sense as donating money to Bill Gates. Vox.com http://slate.me/1jSL56B