JSON serializing an object with function parameter

I have this C# object:

var obj = new {
    username = "andrey",
    callback = "function(self) { return function() {self.doSomething()} (this) }"
}

I need to JSON serialize it to pass to the browser in ajax call. I use JavascriptSerializer, but it serializes to the following JSON:

{"username":"andrey", "callback": "function(self) { return function() {self.doSomething()} (this) }"}

but what I need is:

{"username":"andrey", "callback": function(self) { return function() {self.doSomething()} (this) }}

• no quotes around function definition.

Right now, when the JSON object gets to the browser and is created, the 'callback' parameter is not a function but a string. Any idea how to fix it, preferably on the server side?