function User( username, date_inactive, date_active ) {
    this.username = username;
    this.date_active = date_active;
    this.date_inactive = date_inactive;
};

User.prototype.inactivateMe = function() {
    json_responses.push( this );
    $.getJSON( "url" + this.username, function( json ) {
        original = json_response.pop();
        //do update here
    });
};

userModel = [  ], //Where the loaded usernames are stored.

viewUserModel = {
    users: ko.observableArray(userModel)
    //.......

    //This is how I'm adding users to the array.
addUser: function () {
    $.getJSON( "url",
    { username: usern },
        function( json ) {
            if( json.STATUS != undefined && json.STATUS == 'success' ) {
                newuser = new User( json.USERNAME, json.DATE_ACTIVE, json.DATE_INACTIVE  );
                viewUserModel.users.push( newuser );
            }
        }
    });
    }

function User( username, date_inactive, date_active ) {
    this.username = username;
    this.date_active = ko.observable(date_active);
    this.date_inactive = ko.observable(date_inactive);
};

<div data-bind="foreach: Users">
    <input data-bind="value: date_active"/>
    <input data-bind="value: date_inactive"/>
<div>​