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* 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.

*also available in ShareCG, DAZ, and HiveWire3D flavours (the DeviantArt and CGBytes flavour have been discontinued).