Instead of spending time and effort to persuade people to throw their votes away, spend time and effort changing the voting system so that voting for third parties isnt as futile as FPTP. In the European parliament, the members belong to approx 160 different parties. In the US, you have 2. It has been known for a long time that FPTP converges to 2 (Duverger's law). It makes no sense to keep FPTP but then make voters responsible for the unhealthy situation that emerges from it and persuade them to change their voting behaviour knowing that it makes no sense for them to change it.