LHC,
Not sure if you're aware of it, but that is precisely what the Roman Catholic Orthodox position is on the subject of Christ's human nature. It necessarily means for Christ o be born with a sinless human nature, Mary would have had to have been so born...and likewise all the way back to Eve. The logic of that position must ultimately exclude women from being sinful, because Eve wasn't could not have been included in the legacy of sin - unfortunately, this is also quite contrary to the pronouncements of God in Genesis 3 in her pain during childbirth and in predicting her desires to dominate her man, but ultimately being subject to him instead.
Hebrews 2:14 states that Christ partook of the same flesh and blood as the children. Verse 17 continues to say He was made in all things like unto His brethren, so that He could be the merciful and faithful High Priest as well as to be the propitiation for the sins of the people.
Hebrews 4:15 says our High Priest (who was made in all things like His brethren) was tempted in all things like we are tempted, yet was without sin. Our strongest temptations do not come from outside ourselves, but from within. This is where Christ says the murders, fornications, adulteries, stealing, etc., all originate:
Mark 7:20-23 - "And He said, “What comes out of a man, that defiles a man. For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man."
James 1:14-15 confirms this by describing the exact process of how we sin - "But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death."
If Christ had not stepped in as mankind's Redeemer, that death would have been the irreversible second death - even as far back as Adam (making the human race null and void even before there was a human race).
Christ had to be made fully human (as we are) to reconnect the human race back to the Source and Author of Life. It required Him to become as One with the sinful human race (Hebrews 2:11), as He was One with the sin-consuming Holy Father (John 17:22). I cannot see it happening any other way in order for Christ to be the satisfactory propitiation for our sin. Adam prior to his Fall had no need to be re-connected back to God - he had the original connection intact. Once trashed, that original connection Adam had could not be restored. Adam had to be re-connected through Christ, just as we.
It literally boggles my mind what the Word says had to happen, for us to even have the offer of grace and eternal life given to us.
Blessings,