Subliminal Persuasion: best chances of success
For the sake of "Hail Mary" answers: there's a recent (2016) paper by Ruch et al. claiming unprecedented results:


  Subliminal influence did not significantly decay if probed after 25 versus 15 min. This is unprecedented evidence of the longevity and impact of subliminal messages on conscious, rational decision-making.


You could try to replicate their experiment(s).