outsource XXX.db.bson_serializer.ObjectID.createFromHexString(id) to a function?

I went through this express tutorial. I was wondering if it is possible to outsource the following call to a separate function, as it is very very long?

employee_collection.db.bson_serializer.ObjectID.createFromHexString(id)

This is the whole file where the statement is called:

var Db = require('mongodb').Db;
var Connection = require('mongodb').Connection;
var Server = require('mongodb').Server;
var BSON = require('mongodb').BSON;
var ObjectID = require('mongodb').ObjectID;

EmployeeProvider = function(host, port) {
    this.db = new Db(
        'node-mongo-employee',
        new Server(host, port, {}),
        {safe: true}
    );
    this.db.open(function(){});
};

...

// find an employee by id
EmployeeProvider.prototype.findById = function(id, callback) {
    this.getCollection(
        function(error, employee_collection) {
            if( error )
                callback(error)
            else {
                employee_collection.findOne(
                    {_id: employee_collection.db.bson_serializer.ObjectID.createFromHexString(id)},
                    function(error, result) {
                        if( error )
                            callback(error)
                        else 
                            callback(null, result)
                    }
                );
            }
        }
    );
};

...

exports.EmployeeProvider = EmployeeProvider;

It's the controller of an express application. It's shortened, but should give you an idea of what it does. You can find the whole application on Github.

I tried

getid = function( employee_collection, id ) {
    return employee_collection.db.bson_serializer.ObjectID.createFromHexString(id);
};

and called the function with

{_id: getid(employee_collection, id),

but I'm getting a very long ENOENT error with that one.