Hi Rowan,
I don't know whether or not you're still active, but for anyone else looking for a solution to a similar problem I'll break down the solution.
In this line : Wrapper.instance.bindSetter("Services.employee.empName", empNameSetter);
You are calling the empNameSetter function but aren't passing an object.
private function empNameSetter(value:Object):void{
//code goes here
}
You should either pass an object to your function in the function call like so:
Wrapper.instance.bindSetter("Services.employee.empName", empNameSetter(ObjectGoesHere));
or
Modify your declaration not to take any parameters.