Having never tried spacers, and not having stock studs, I'll just say that the general rule for "safe" is to have as many millimeters of threads engaged as the stud is wide. That is, for a 12x1.25mm Nissan stud, you want 12mm worth of threads engaged by the nut. In this case, that's 10 full turns.

If I don't see you at QSL, I'll just assume that your wheels fell off!