I think your example with fetuses being the variation between single cells and adults is very adequate here. So my claim would probably be something along the lines of "the fact that 8-month old fetuses exist (which usually may not be killed anymore) is a strong reason why in most countries 4-months-old fetuses have a lot of legal & societal protection. If there was nothing in between the 4 months fetus and the born baby, I don't think many countries would ban abortion of 4-months old fetuses, rather it is there because of the transition. Thus the existence of a smooth transition between non-human animals and sapiens would increase support for "lower" animals.
I agree that there is already a continuum with e.g. disabled sapiens as you name it. However I don't think that "commonsense" is aware of that. I think commonsense sees mentally disabled people as something "that could have been any of us" (or could even still happen to many of us, as some mental disabilities are not from birth). However intermediate species can not be considered disabled exceptions/"misfortunes" or something like that
Does the CEO have to be based in the UK or is willingness to travel a lot sufficient?