He was fully God. He was fully God dwelling within the constrictures of time. Thus he could know the past (which he demostrated quite aptly) but could not know the future, except that which was revealed by the father (who was dwelling in eternity).
If Christ was fully God and fully Man... then your theory would appear to suggest that Christ was incarnate before Christ was incarnate.
The statement that he was crucified before the foundation of the earth would make that implication a lot stronger than any statement that I have made. Christ was not incarnate until the moment of his incarnation. That, from our view occurred 2000 years ago. But from the point of view of God dwelling in eternity, that event would been observed from before the foundation of the earth, since in God's eternity all events past present and future are within his realm simulatanously. There is no point, past, present or future that God does not inhabit.
Our limitation is that we, as creation, must view the universe as being linear, starting at one point and going forward from there. But God, being the creator of all things, would obviously view it as circular, starting nowhere in particular and never ending.