How to map objects from xml back to original.

We have a webservice which takes as an argument someobject for example.

WeServiceMethod1(CustomObject objectArgs);
The CustomObject represents a class from  a library referenced by the webservice. We have a client app that calls this webservice and passes it the object CustomObject.


The client app only knows about the object that it builds by calling wsdl after creating a reference. So for example it will be contained in the namespace of the created web reference. Well that would be fine however we want to deploy the original object [that the web service is using as an argument] into the client app so that it can use it before sending it. But is there an easy way to convert between the actual original object and the object that the client app will see from the reference. They are in essence the same thing?...Or do we need to create a conversion interface for the two objects?...
Any help much appreciated into what the best approac is o ...