MMmm...interesting. If I recall the wording of SB23, the passage in question goes something like this:
12276.1 (a) Notwithstanding Section 12276, "assault weapon" shall also mean any of the following:
(1) A semiautomatic, centerfire rifle that has the capacity to accept a detachable magazine and any one of the following:
(A) A pistol grip that protrudes conspicuously beneath the action of the weapon.
(B) A thumbhole stock.
(C) A folding or telescoping stock.
(D) A grenade launcher or flare launcher.
(E) A flash suppressor.
(F) A forward pistol grip.
So lets see... I suppose the argument could be made that what you propose is *not* a pistol grip, even though it does protrude below the action. It's definitely not a thumbhole stock...
We need someone who's better with the laws. Paging Jim March. Mister March, please pick up the phone.