Brian Wilson's guide shows how to do this. The guide is for VS2010, but it worked fine for me in VS2012.
The main steps:
- Set up the environment variables using "c:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\Tools\vsvars32.bat"
- Edit C:\7zsrc\CPP\Build.mak to remove "-OPT:NOWIN98" from line 34
- Run C:\7zsrc\CPP\7zip\nmake NEW_COMPILER=1 MY_STATIC_LINK=1
Note the third step targets the makefile in the 7zip subdirectory instead of the Build.mak that you are targeting.
A number of executable are created. You may be interested in C:\7zsrc\CPP\7zip\UI\Client7z\O\7z.exe