php5 soap client and classmap

Hi list, when i call a webservice wich return a complexe structure , i can define a classmap option to cast the returned object to a defined class. In my case, the returned object contains a collection of other objects that i would like to cast too. But i can't manage it to work. Maybe somebody knows how to do that? my return object is something like: Order ( casted as CustomOrder via classmap) |___ OrderItems ( a collection of items)---------OrderItem ( currently seen as standard class object and i would like to cast it to CustomOrderItem)

                                                          ---------OrderItem

Thanks in advance xavier