Even if it was to help them in a Democratic primary, in the general election being a Muslim would most likely hurt them among evangelical Christians and other demographics who wouldn't be fond of having a Muslim president. I could easily see Trump winning 75 or 80% of the vote in states like West Virginia.
They could convert to Islam for the primaries, then flip-flop back to Christianity for the general election. Maybe that's too big a shift to be believable though. How about some kind of moderate hero stance on Jesus's divinity?