Use the opportunity to get into a huge religious debate, hardly dinner conversation. After all, they invited you over under false pretenses and then brought up religion at the dinner table. Get on about how the bible is a sham, and the Mormon faith is truly for morons.
Get all schooled up on Mormons, real facts. Watch them squirm as you shed light on their silly beliefs and pick them apart piece by piece.
OR you could take your wife out to a nice dinner and movie instead. I'd love to go in your place, just to have the opportunity you have.