you could use an object merge, point it to the "camOrigin" node inside of your camera, change the "transform" option to "into this object", and pipe the ouput of the object merge into the second input of your attribute vop. Then in the attribute vop you could access the second input with an "Import Point Attribute" and change the input parameter to "second input", and pipe a constant of 0 into the "ptnum" parameter.
-G