Modularizing Socket.io with Express 4

I'm trying to modularize my application files and I'm having problems with Socket.io. I would like to use the io inside my routes.js. Something like this:

var router = require('express').Router();
var io     = require('./sockets/my-io');

router.get('/', function(req, res) {
  io.emit('request-detected');
});

module.exports = router;

But I can't do, because the socket.io needs the app server, and when I'm inside the routes.js file, the app server is not listening or being exported yet.

Can you give me a solution, or any other approach to this problem?

Here's what I have:

app.js

var app = require('express')();
var routes = require('./routes');

/* ... */

app.use('/contacts', routes);

module.exports = app;

bin/www

#!/usr/bin/env node

var app = require('../wallet');

var server = app.listen(port, function() {
  debug('Express is listening o port ' + port);
});

routes.js

var router = require('express').Router();

router.get('/', function(req, res) {
  console.log('hey');
});

module.exports = router;