how to copy a single file in each directory

Question

I would like to configure and execute a task that copies a specified file in each dir recursively. In specific I would like to have "index.php" copied in each directory and subdirectory of my web project, if that doesn't exist. I've tried to use multidest and copy but multidestdoesn't seem to allow to specify paths by means of a wildcard (too bad!). How could I solve this? Thank you

grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),

    multidest: {
        tst: {
                tasks: ['copy:indexphp'],
                dest: '**/' //THIS DOESN'T WORK, I SHOULD SPECIFY ANY DIR/SUBDIR/ETC.. 
        },
    },

    copy: {
        indexphp: {
            expand: true,
            cwd: 'classes',
            src: 'index.php',
            filter: function (filepath) {
                // NPM load file path module.
                var path = require('path');

                // Construct the destination file path.
                var dest = path.join(
                    grunt.task.current.data.dest,
                    path.basename(filepath)
                );

                // Return false if the file exists.
                return !(grunt.file.exists(dest));
            }
        },
[...]