Yes, he extrapolated the part about the extra Body based on the fact that we believe the Romans were not yet saved.
It's not so hard to see that they weren't saved at the writing of it, but became saved because of the writing of it as God foreknew they would believe!
Romans 11:1 I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin.
Romans 11:2 God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying,
Romans 11:3 Lord, they have killed thy prophets, and digged down thine altars; and I am left alone, and they seek my life.
Romans 11:4 But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal.
Romans 11:5 Even so then at this present time also there is a remnant according to the election of grace.
Romans 11:6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.