Sometime ago, Bantha put together a gamma correction python script which installs the necessary shader nodes.  They do plug into the alt_diffuse of the root node.  Very convenient and handy.  Used it several times in P8 before PP 2010.  I thought it was posted in the free section, but haven't found it.  I do know it was posted here in the forum last year.  Perhaps, if you get in touch with him, he would be more then happy to release it again.

And BTW, if you do begin to use it on a regular basis for everything, you will need to drop your light intensities.