inject.js

var source = require('vinyl-source-stream')
var buffer = require('vinyl-buffer');
var queue = require('streamqueue');

gulp.task('shit', function(){
  // make the fake file
  var fakeFile = source('fake.js');
  var buffered = fakeFile.pipe(buffer());
  
  // join the streams
  var all = queue(
    gulp.src('files/*.js'),
    buffered,
    gulp.src('files2/*.js')
  )
    .pipe(concat('all.js'))
    .pipe('./dist/');
    
  fakeFile.end(new Buffer('a string'));
  
  return all;
});