Just a couple of point on this.
The JavaBean specification does not requite a getter and setter for each property. A get method implies a readable property (in Axis terms, it means that property can be serialised). A set method implies a modifiable property (in Axis terms, it means the property can be deserialised).
Simon mentioned a special constructor on BeanSerializer and BeanDeserializer. If this can be used to do what Tim wants, only BeanSerializerFactory and BeanDeserializerFactory subclasses would be needed, to create the appropriate instance, and specified in the mapping. However, a quick scan of the BeanDeserializer indicates that it might not do the job - sorry, if I've got that wrong.
Tony