That's part of the reason I'd regard implantation as more of a 'landmark' than fertilization. I personally would regard an unimplanted embryo as being equivalent to an acorn: it is a genetically unique product of sexual reproduction, but it has not yet reached the point of development where it must forevermore either grow or perish. An acorn isn't considered a living tree until it enters the ground and germinate; I would apply a similar standard to human development.
I would also point out to my friend that to crush and dispose of the raw peanut is to end the life of an individual peanut plant at that individual plant's early age. If we look at the individuality of a zygote, to purposely kill that living zygote we have ended the lifetime already begun for the human being that is that zygote at that age in its lifetime continuum already begun.
Lastly, I would note for my friend that neither of us can say at what developmental age the human soul is present with the human body such that we can precisely say the soul was not present with that body moments before that instance. Since the scriptural reading states that God knits us together - body and soul, I would take Him at His word, that He is knitting together body and soul and I ought not be for disposing of His 'yarn'.