CMD /c vcvarsall.bat x64 && set
Then dump the VC specific environment variables in a file and you are good.
I implemented this in tundra a very nice and fast build system. It's in Lua... you can look at it here https://github.com/deplinenoise/tundra/blob/master/scripts/t...
The problem this code is solving is equivalent to finding vcvarsall.bat in the first place.
Also, if you want to run that command you need to run it from the developer command prompt. Otherwise it's location isn't in your path but like I said this script is always in the same location and what it does is that it sets up the environment for you and it's configurable via parameters.
I am well aware that you can use the developer command prompt (in which case you don't need to run that command at all, it would be redundant). But it's a ridiculous and extremely annoying requirement to impose on your users.