yo haría algo mas simple. pasarle una variable
Cita: function employee(name,jobtitle,born){
this.name=name;
this.jobtitle=jobtitle;
this.born=born;
this.callme = function(op){
this.opcion = op || 'original';
return this.opcion;
}
}
var fred=new employee("Fred Flintstone","Caveman",1970);
fred.callme('alternativo')