There's a compile option called "-wadinclude" for the csg part of the compile process. To embed all used textures from a certain wad into the .bsp, put this on the csg command line: -wadinclude [yourwadnamehere].wad. Just embed custom textures, though, because everybody will have the textures that come with NS.
if you're using batch compiler, tick one of the wad include boxes on the CSG tab and browse to the wad. if you're using a batch file, add "-wadinclude <wadpath>" to the CSG line. if you're using Hammer to compile, add "-wadinclude <wadpath>" to the parameters line for CSG.
Under "Compile/Run Commands" click on the "$csg_exe" line, then in the box above marked "Parameters" add that to the end after what is already in there.
Comments
if you're using a batch file, add "-wadinclude <wadpath>" to the CSG line.
if you're using Hammer to compile, add "-wadinclude <wadpath>" to the parameters line for CSG.