After a bit more thought I have a potential answer - 15 nodes, but you have to manually enter the camera's x, y, and z coordinates into three nodes.

I've posted my possible solution to my "Distance From Camera To Point Being Rendered ?" thread in RDNAs Node Cult forum

http://forum.runtimedna.com/showthread.php?104645-Distance-From-Camera-To-Point-Being-Rendered

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.