Nope. Says born, and "before I formed you in the womb" implies there's something there to form.
“Before I formed you in the womb I knew you; Before you were born I sanctified you; I ordained you a prophet to the nations.” - Jeremiah 1:5
http://www.biblegateway.com/passage/?search=Jeremiah1:5&version=NKJV
"Formed" in that verse is the word yatsar, meaning to mould or to form.
If it was conception, the word would have been harah.
Verse 11?
(for the children not yet being born, nor having done any good or evil, that the purpose of God according to election might stand, not of works but of Him who calls), - Romans 9:11
http://www.biblegateway.com/passage/?search=Romans9:11&version=NKJV
Gennao means to be born, or to be begotten. It is not translated as "concieved" in the Bible.
Then he said, “Hear now, O house of David! Is it a small thing for you to weary men, but will you weary my God also?Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel.Curds and honey He shall eat, that He may know to refuse the evil and choose the good.For before the Child shall know to refuse the evil and choose the good, the land that you dread will be forsaken by both her kings.The Lord will bring the king of Assyria upon you and your people and your father’s house—days that have not come since the day that Ephraim departed from Judah.” - Isaiah 7:13-17
http://www.biblegateway.com/passage/?search=Isaiah7:13-17&version=NKJV
Considering that God knew God the Son already prior to His incarnation, because He existed BEFORE the incarnation, I'm gonna go ahead and throw this one out, as God announcing His plans for His Son, who is God, it's a completely different situation, as there was never a point where the Son never existed. Humans are different, in that our existence begins at conception.
So, all God needs to do is tell the future Josiah's parents to name him Josiah, and then guide Josiah along in life.
How is that knowing Josiah before-hand?