How to get a gulp stream from a vinyl object?

How can I create a stream using a vinyl object so I can use gulp.js plugins on it?

var file = getFoo();  // An in-memory file as a vinyl object.
return gulp.src(file) // What to do here? gulp.src only accepts globs.
    .pipe(css())
    .pipe(gulp.dest('...'));

via Şafak Gür