Avoiding the Bc4 Grand Prix attack at the cost of being move ordered out of the Najdorf seems more than a little bit like cutting off one's nose to spite one's face.  The GP with Bc4 isn't great anyway, and certainly shouldn't scare a well-prepared player.  It's a good version of a line where the good versions are = anyway.  2...d6 is the move order.  I vaguely remember there are other problems with 2...a6, anyway (White gets a good Morra Gambit, Alapin, or Hedgehog), so it isn't like that's a way to avoid bad versions of sidelines.

Exception: If you only play the Najdorf to get a Scheveningen w/o the Keres, the best move order is probably 2...e6, which is probably the best second move for dealing with anti-sicilians (you have to be willing to play an Advance French every blue moon or so, but that's easy to learn and decent for Black).  You have to be willing to play with ...Nc6, but that's okay.  If you're looking to get Najdorf main lines rather than Scheveningen stuff, though, you need to play 2...d6.

e.g.:

1 e4 c5 2 Nf3 e6 3 d4 cxd4 4 Nxd4 Nf6 followed by ...d6.
1 e4 c5 2 Nf3 e6 3 c3 d5 4 e5 Nc6 5 d4 (the aforementioned transposition)
1 e4 c5 2 Nf3 e6 3 c3 d5 4 exd5 exd5 is probably going to be an IQP position, but one which should be A-okay for Black since White is committed to c3.
1 e4 c5 2 Nf3 e6 3 Nc3 Nc6 4 g3 Nf6 heads for the lines of the Closed where Black plays f7-f5 in response to g4.  This is okay for Black, although it isn't my favorite position to play.
1 e4 c5 2 Nf3 e6 3 Nc3 Nc6 4 Bc4 Nf6 5 [anything but d2-d4] d5.

Being serious now, Gelfand (a principled najdorf player) has always played 2...d6 not fearing the Grand-prix too much.

After 2......Nc6 you can still play a Najdorf.  Look at some of the older lines where 6.........Nc6 is played or maybe even before that.  One developing move cannot take you out of the Najdorf as it is a flexible system designed originially to be played with e5 rather than the current schevengin fashion.   

Look at some older games and you will find plenty of times in the Najdorf where Nc6 is useful and you can always redeploy the N via e5 where it goes alot of times from d7 anyways.   

Just my 2 cents.

There is also however some other stuff (the line with Nxc6 and e5, and White aiming to transpose to the Classical Dragon, though in the latter case Black has some independent tries).

1.e4 c5 2.Nc3 Nc6 3.Nge2 d6 isn´t possible since he wants to play a Najdorf...

3... e5 is solid and fully playable but Black will find it difficult to play for a win.

I don´t now if this has been covered in any book so far. Perhaps by Rogozenko in "Anti-Sicilians: A Guide for Black"?

But TonyRo has stated elsewhere he will cover this line for Black in his upcoming book "The Killer Sicilian" published by Everyman later this year.

Why not 3...d6?