I have to say that I side with Sinick on this one. The pureblood wizarding community is just not that large. That's why they all intermarry with each other, as Sirius observes to Harry (when he's explaining that Black family tapestry in book 5): there are so few of them, and they're all interrelated.

So, the "real" pureblood family names are going to be very common knowledge. And so someone could try to hide the fact that he had a Muggle (or Muggleborn) mother, perhaps, and get away with it. But a Muggle father means that your half-blood status will be given away to someone like Lucius, the second you introduce yourself. I just don't see how it could be otherwise, in such a small community.