Generating null object control with animation preset?

I've recently started playing around with expressions and animation presets in After Effects.  I set up some expression controls on a camera's z position and zoom and connected them to a slider in order to recreate the "Hitchcock Pull" effect with a single slider.  My problem is, I can't seem to apply the slider control effect directly onto the camera and instead have to apply the effect to a null object on a new layer.  My question is, is there a way I can save the expression to automatically generate that controlling null object along with the expressions so I can set up this effect in one step without having to manually rebuild the control layer?

The effect:

The setup:

I'm using After Effects CC 2015

I appreciate any help