animating a line that is a 3d layer in after-effects What I'd like to do

I'm trying to draw a 2D smiley face with the pen tool on a 3D layer...and then change it to a frown (or a sad face). I was able to do this in as 2D layer...but I'd need help on doing it as 3D layer.

Why I'm using 3D Layers in the first place

I'm using a camera (attached to a null layer) to zoom in and out of certain images I have in my animation (which are imported from illustrator). I've realized that you have to have 3D layers if you're gonna pan and zoom with the camera tool!

What's the Problem

It's close to impossible to draw using the pen tool if the pen layer is 3D. Even if I do get something drawn, I can't figure out how to animate it as a 3d layer. 

Any tips?
The way I normally go about drawing paths in AE is by using the stroke effect with masks


Create an Adjustment Layer
Create Mask Paths for the smiley face
Add the Stroke effect to the Adjustment Layer 
Make the Adjustment layer 3D and then position it where you want
Animate the Mask Path to animate the mouth



http://i.stack.imgur.com/MF5pX.png

Note: 

For some reason the stroke effect doesnt work on open paths when there is more than one mask on a layer. So I put the eyes on one Adjustment layer, and made a second Adjustment layer for the mouth. Then I turned OFF 3D on the layers, PreComped them together, and made the PreComp a 3D layer. 

Have a look at what I did: http://www.filehosting.org/file/details/334754/Smiley_Face.aep