<< This, of course, is not a problem for Evangelicals since we don't view Mary as the ontological mother of God. >><quoted text>
Fine. Then you should not view the Blood of Christ as the ontological Blood of God either, because He got His Blood from Mary.:-) And if the Blood of Christ is not the Blood of the eternal Son, then you are still in your sins, since no Divine Sacrifice was made for you. If the eternal Person of the Son did not **truly** and ontologically acquire a human mother, then He was not truly and ontologically a human being. Thus, He was not truly and ontologically one of us; thus He could not truly and ontologically die; thus no Sacrifice; thus we are still in our sins. Find a way out of this if you can.:-)
<< She was the mother of Jesus, but only in a provisional and temporal sense. >>
I see.:-) Then Jesus was only a human being in a "provisional and temporal sense"; and so Jesus is no longer a man, and so there is no one-Flesh relationship between Him and His Church (per Ephesians 5:25-32). And, this being the case, you cannot claim the Blood of Christ for your salvation, and so are still in your sins.