I think you have a different concept of 'person' in mind than needed. We can define 'person' as "that which can think, reason, and has personality" or something similar (this is roughly what I think you mean by 'person'), but that isn't really relevant to the question. Like Carl said, we are looking for a value laden definition here - something to tell us whether we should use those embryos or not.
Honestly, all of this definition nonsense is misleading. We don't really care about the definition of 'person.' What we want is to sort out our values. Embryo's certainly aren't in my utility function, and that's all that matters. Defining 'person' is superfluous.
From Michael Eisen's blog:
Yuval Levin, former Executive Director of the President's Council on Bioethics, has an op-ed in Tuesday's Washington Post arguing that Obama's new stem cell policy is dangerous. Levin does not argue that stem cell research is bad. Rather he is upset that Obama did not dictate which uses of stem cells are appropriate, but rather asked the National Institutes of Health to draft a policy on which uses of stem cells are appropriate:
Lost in this superficially unobjectionable - if banal - assertion of the complexity of ethical issues involving science is Levin's (and many other bioethicists) credo: that the moral complexity of scientific issues means that scientists should not make decisions about them.