The only way to be born again is to believe in the death, burial and resurrection of Jesus for sins. Period. This was not possible until after the cross.
7 Marvel not that I said unto thee, Ye must be born again.
8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
9 Nicodemus answered and said unto him, How can these things be?
10 Jesus answered and said unto him, Art thou a master of Israel, and knowest not these things?
11 Verily, verily, I say unto thee, We speak that we do know, and testify that we have seen; and ye receive not our witness.
12 If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you of heavenly things?
13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up:
15 That whosoever believeth in him should not perish, but have eternal life.
16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.