Not sure if this post is naive, but here goes:
I'd follow the trend in social entrepreneurship started by the Grameen Bank (who's founder is a Nobel Prize winner), but apply it to trading. The Grameen Bank gives very small loans ("micro-credit") to women with very small businesses who live in poverty where no loans are available. The bank is profitable and has very high repayment rates.
Assuming you don't have kids in school, then if I were you I think I would travel to a developing country (GDP < 2500/person) where at least 50% of people speak English (or any other language you speak well), and where you can get excellent internet (for a price, to be sure). I would open up a trading office and train individuals from that country to trade on a relatively small-scale.
Why?
1. If you can train an individual to be a net positive trader there, then the impact is huge. Even low wage salaries by our standards ($20,000) would significantly improve the standard of living for large families/communities, as individuals are otherwise only able to find jobs paying < 5000/year. For the trainees who fail, the increased computer literacy and math/financial skills would be beneficial anyway.
2. With the smaller scale trading, the risk is less for the owner than would be in starting an American firm -- the amount of money likely lost on "blow ups" is relatively small. The start up cost is relatively low (cheap property, cheap wages prior to profitability)
3. There is likely very smart, very hard working, very hungry, untapped talent in these areas, with a lack of opportunities to make money based on merit.
4. The standard of living increase for successful traders/their communities would matter for real.
5. If it works out and the office grows over time, it'd be profitable.
6. If it fails miserably, you just got a first hand look at the actual value of all those dollars you own and installed good internet somewhere without it.
Example place to do this: Georgetown, Guyana (it borders Brazil)
