Pretty sure the status of the child follows that of the mother for an out of wedlock birth. That is, if the mother is a citizen, and the child is born in the country, then the child is a natural born citizen.
There's Obama's fall-back position--have his mother's marriage to Barack Sr. declared null and void because his father was married to someone else at the time. If that doesn't work, claim that Frank Marshall Davis was his real father.
Of course, this is assuming that Barack Jr. was born in the US.