If two babies are born at the same time beside each other, and one of them is severely mentally retarded and will always be........... and the other is fully statistically "normal" in every way......... I would not, for example, suggest either one of them has more of a "right to life" than the other. And I would likely say that again if I came back 5 year later and met them, 10 years, 20 years, and 50 years. I simply do not argue on potentials. I argue solely on what is THERE.
So I am afraid how I really feel is entirely independent of what you are "ready to accept" about how I really feel.
But in the contrived and specific situation YOU describe...... I not only find the frog more morally important, but I would think continuing with your scenario to be positively immoral. A) Because of using an essentially dead body as an incubator and B) because contriving to bring a human person into being who has no relatives or connection with this world to be a horrible idea. You end with the line "no one personally concerned with the death of this fetus" but I would be more concerned with "no one personally concerned with the LIFE we would create" as being the situation we would be forcing on the person we aim to create.