Like you, I am evangelical and recognize the LDS teachings as not being compatible with Christianity. Regarding conversion, that is his decision and not yours or mine to make on his behalf.
I hope things work out for you professionally. I remember when I was your age I sympathized with your point of view until I read more Locke, DeTocqueville and others. That coupled with paying taxes in the real world solidified my belief in conservatism. If I were you, go read mark Levin's Liberty and Tyranny. It will open your eyes. Best wishes!