I don't say he speaks those words AS as sinner, himself. He speaks them in my place. Christ is a "publick" person, he's a Representative.
Do you think that for him to say those words would make him a liar; he can't lie; ergo, he cannot say them? In that case, how can he even go to the cross? What is the division between words and actions?
That is an interesting thought; I shall have to ponder it.