Stay wide open?
Actually, there's a trick that works with Canon EF lenses that might work with Nikons as well. You have attach the lens to the SLR body, set the aperture, press the DOF preview button and remove the lens while holding it. This way the aperture stays at the selected value. Not very convenient for run and gun shooting, but works.
i don't know about tokina with nikon mounts.
but nikon lenses that do not have manual aperture ring - you can put a bit of a match stick (or tape) the prong on the mount to stop it from auto closing up.