A few workarounds spring to mind: 1. Run challenge trials, but don't pay participants in money. Talk up the danger and risk, and publicize the heroism of the p

A few workarounds spring to mind: 1. Run challenge trials, but don't pay participants in money. Talk up the danger and risk, and publicize the heroism of the people who volunteer. Make a spectacle of it. If you ask for fifty heroes, is there any doubt that you'd get them? 2. Pay participants, but impose a minimum price they need to be paid in order to assuage people's squeamishness. That hypothetical guy in sub-Saharan Africa might be exploited at $10, but if he's getting paid $1,000,000 then he has practically won the lottery. Either of these would be a big improvement over the status quo, where challenge trials aren't run at all and countless people die because of it.