There does not appear to be a way to do this, in such a fashion as to no longer require Visual Studio 2005.
You can, however, use registry hacks to force Visual Studio 2012 to build a WinCE 5.0 project by utilizing the compiler binaries from Visual Studio 2005, during compilation. This would allow you to develop code in VS2012, but would also require that VS2005 be installed for a successful build.