What prominent Christian thinkers (if any) held to polygenism and if so how did these thinkers view original sin?

Yes. In his book, The Problem of Pain, popular Christian author C.S. Lewis discusses Adam's sin in the context of Scientific understanding of his time, which included Darwinism. He presents an understanding in which those creatures, guided by the hand of God, became man. Despite Lewis' prominence in twentieth century Christianity, this particular viewpoint of his is not a widely celebrated one:

...The Fathers may sometimes say that we are punished for Adam's sin: but they much more often say that we sinned "in Adam". It may be impossible to find out what they meant by this, or we may decide that what they meant was erroneous. But I do not think we can dismiss their way of talking as a mere "idiom". Wisely, or foolishly, they believed that we were really and not simply by legal fiction - involved in Adam's action. The attempt to formulate this belief by saying that we were "inAdam in a physical sense - Adam being the first vehicle of the "immortal germ plasm" - may be unacceptable: but it is, of course, a further question whether the belief itself is merely a confusion or a real insight into spiritual realities beyond our normal grasp. At the moment, however, this question does not arise; for, as I have said I have no intention of arguing that the descent to modern man of inabilities contracted by his remote ancestors is a specimen of retributive justice. For me it is rather a specimen of those things necessarily involved in the creation of a stable world which we considered in Chapter II. It would, no doubt, have been possible for God to remove by miracle the results of the first sin ever committed by a human being; but this would not have been much good unless He was prepared to remove the results of the second sin, and of the third, and so on forever. If the miracles ceased, then sooner or later we might have reached our present lamentable situation: if they did not, then a world, thus continually underpropped and corrected by Divine interference, would have been a world in which nothing important ever depended on human choice, and in which choice itself would soon cease from the certainty that one of the apparent alternatives before you would lead to no results and was therefore not really an alternative. As we saw, the chess player's freedom to play chess depends on the rigidity of the squares and the moves.

Lewis refers to this as the "true import of the doctrine that man is fallen."

...Science, then, has nothing to say either for or against the doctrine of the Fall. A more philosophical difficulty has been raised by the modern theologian to whom all students of the subject are most indebted. This writer points out that the idea of sin presupposes a law to sin against: and since it would take centuries for the "herd-instinct" to crystallise into custom and for custom to harden into law, the first man - if there ever was a being who could be so described - could not commit the first sin. This argument assumes that virtue and the herd-instinct commonly coincide, and that the "first sin" was essentially a social sin. But the traditional doctrine points to a sin against God, an act of disobedience, not a sin against the neighbour. And certainly, if we are to hold the doctrine of the Fall in any real sense, we must look for the great sin on a deeper and more timeless level than that of social morality.

...For long centuries God perfected the animal form which was to become the vehicle of humanity and the image of Himself. He gave it hands whose thumb could be applied to each. of the fingers, and jaws and teeth and throat capable of articulation, and a brain sufficiently complex to execute all the material motions whereby rational thought is incarnated. The creature may have existed for ages in this state before it became man: it may even have been clever enough to make things which a modern archaeologist would accept as proof of its humanity. But it was only an animal because all its physical and psychical processes were directed to purely material and natural ends. Then, in the fullness of time, God caused to descend upon this organism, both on its psychology and physiology, a new kind of consciousness which could say "I" and "me", which could look upon itself as an object, which knew God, which could make judgements of truth, beauty, and goodness, and which was so far above time that it could perceive time flowing past. This new consciousness ruled and illuminated the whole organism, flooding every part of it with light, and was not, like ours, limited to a selection of the movements going on in one part of the organism; namely the brain. Man was then all consciousness.

... We do not know how many of these creatures God made, nor how long they continued in the Paradisal state. But sooner or later they fell. Someone or something whispered that they could become as gods - that they could cease directing their lives to their Creator and taking all their delights as uncovenanted mercies, as "accidents" (in the logical sense) which arose in the course of a life directed not to those delights but to the adoration of God.