Without looking like a flip-flopper and undercutting the message that he’s been running on since the beginning of his campaign. If Romney used this part of David’s speech, he would seriously be backtracking on the whole social issues he’s been running on (and using in his campaign ads):

We have gotten the God of Life and the God of politics confused. We have gotten the prince of this world confused with the Prince of Peace. Only faith can tackle America’s biggest problems – broken families and broken hearts and broken bodies. Those things that eat at America’s soul – divorce and abortion and illegitimate births and drugs and abuse – those things are largely beyond government’s reach. Lord knows we have tried and tried and tried to make the government conquer those things – even those who call themselves “conservatives.” But we need to take a step back now and say that government cannot do but the people of God can.

I don’t think Romney would be stupid enough to give that much of a leverage to Huckabee, especially since Huckabee appears to be the only social conservative alternative to Romney. (Though, I have to say, I wish someone would give that speech, it really does need to be said.)
Ultimately, I don’t think Romney could give a speech about the distinctives of his faith because if he did it would undermine the bridge that he’s been building to the Christian community. It’s a Jesus bridge that can’t be sustained when you really look at what Mormons believe.
He could and should give a speech in which he makes it clear that faith shouldn’t be an issue in which we decide who is president. A Mormon can be an advocate for life, a Mormon can be an advocate for the family, a Mormon can love America and what to defend it just as much as a Christian. A Mormon can understand his responsibility to guide and protect this nation and uphold the constitution in the same way a Christian can. Giving a speech about faith instead of Mormon distinctives would get the issue off the table without giving detractors ammunition.