This whole plan is ... dumb. Even if he falls for Ebino he would still be able to see Eve floating asleep above his own head reminding him of his first love. Not to mention that when the plan fails, and it WILL fail, Ebino gets hurt again. This plan solves nothing except satisfying the needs of everyone ... except for Eve. If Ririsu would be honest Eve would achieve the happiness she deserves. She can break up with Larou after the fact.
Also, I've said it before and I'll say it again ... Eve is Ririsu's face with Ebino's body. Tarou is physically attracted to Ebino while being emotionally attracted to Ririsu.