Set Sdk40ToolsPath
rather than SdkToolsPath
to specify a location other than the install directory.
I hit a similar problem with AL.exe because I had just xcopied the tools onto the build machine rather than installing the SDK, so the usual registry keys were missing. I ran a build with diagnostic output (/verbosity:diagnostic) and noticed that there were several SDK tools paths defined: Sdk40ToolsPath, Sdk35ToolsPath and SdkToolsPath. Setting Sdk40ToolsPath to point to the appropriate SDK version's bin folder solved the problem for me.