How can I move CornerPins to the exact points when a layer moved into Z space to align it with comp?

If I'm reading your post correctly - you want to match the corner pins of a layer in 3D space with the corners of another 2D layer? The best way to do this is with layer space transform expressions - but this is a complex area.

Lets's call your layer: "solid2D".  On your upper left corner property paste this expression:

S2D = thisComp.layer("solid2D"); //get the name of the layer.
S2DP = S2D.toComp([0,0,0]);      // get the layer's upper left position in Comp space.
fromCompToSurface(S2DP)          // project that Comp position onto the surface of the 3D layer.

You will need to adjust the layer name: "solid2d", to your own layer name.

That should give you a matching position for the upper left corner pin.

For the other corner pins replace the second line of the expression as follows:

for upper right:

S2DP = S2D.toComp([S2D.width,0,0]);

for lower left:

S2DP = S2D.toComp([0,S2D.height,0]);

lower right:

S2DP = S2D.toComp([S2D.width,S2D.height,0]);

I hope the above helps! 

It's a cosine transform based on the distance and zoom level.

Mylenium