Server-side model change event in DerbyJS 0.6

In DerbyJS:

How do I add event listeners to "The Model", only server side, without having to rely on requests (express middleware)?

Related question I've found: How to create server-side application logic on Racer / DerbyJS?

Of course I can write an express middleware. But the "shared" data model would come in really handy if I could access it without having to rely on a request, and I don't know how to do that without having to put the specific code into the shared codebase.

Use case: order processing for e-commerce software

My model could be like this:

{
  orders: [ {
    id: '1',
    products: [ ... ],
    user: [ ... ],
    token: 'stripe credit card token I get from Client here'
  }, {
    ...
  } ]
}

This way the client could place new orders doing

model.at('orders').add(myOrder);

And the server could process it by listening for 'insert' events:

model.on('insert', 'orders', function(captures, index, newOrders) {
  newOrders.forEach(processOrder);
})