In this ground-breaking study, it was found that pressing your tongue into the roof of your mouth increased power production on isolation exercises significantly more than other tongue positions. This may be due to a unique interaction between the tongue and CNS. This also may only work on isolation exercises, more research definitely needs to be done. Try it out and let me know what you think!
Reference: di Vico, R., Ardigò, L. P., Salernitano, G., Chamari, K., & Padulo, J. (2013). The acute effect of the tongue position in the mouth on knee isokinetic test performance: a highly surprising pilot study. Muscles, Ligaments and Tendons Journal, 3(4), 318.