If your friend is already well read in Scripture, you could try introducing him to the early Fathers, to show how the earliest Christians read Scripture. This was the universal Faith of the ancient Church was, even in the generation immediately after the Apostles, or even during their lifetimes, many of whom had heard the Apostles preach.
Since you speak of the Real Presence, St.Ignatius of Antioch (circa 110 A.D.) is typical,
Take note of those who hold heterodox opinions on the grace of Jesus Christ which has come to us, and see how contrary their opinions are to the mind of God ... They abstain from the Eucharist and from prayer because they do not confess that the Eucharist is the flesh of our Savior Jesus Christ, flesh which suffered for our sins and which that Father, in his goodness, raised up again. They who deny the gift of God are perishing in their disputes.
This shows that the early Christians took Our Lord (Jn 6:53-58) at His word. He repeated it very clearly and very plainly for them and for us. The Holy Eucharist is the sacrifice of the Messianic dispensation that Malachi foresaw (Mal 1:11-12) offered by Gentiles universally.
Will pray.