As an aside, I don't have a problem with cmake, except that it is pointlessly hard to get the equivalent of 'configure --help': you have to make a new directory, cd into it, then do ccmake .. and hit 'c', then note down the flags you want, quit, and wipe the directory (assuming you want to note those flags down for your autobuilder rather than make it by hand).
But as for supporting an equivalent of config.site... well, all my config.site does is runs a shell script under 'eval', passing in as arguments those 'variables set by options' by configure whose default value is non-NULL. All I have to do for cmake is arrange for my autobuilder to add default arguments to the cmake invocation which are computed by calling the same shell script and doing a few trivial transformations of the output with sed (to change configure-style variable names to cmake-style command-line arguments). This is not hard. My configure-running script is 85 lines; my cmake-running script is 32, mostly comments. I don't see the point of whining over 32 lines and half an hour's shell script hacking.