WCF: XmlNode as a parameter in method (or property in contract)

Question

At this moment I try to move from ASP.NET WEb Services to WCF (using basicHttpBinding). In asmx services I used XML node as a parameter in my methods, but now it is a problem. I get DataContract Serializer Exception - xmlnode can't be serialized when I try to provide XMLNode parameter in DataContract. Is there any way to use XML node as a parameter? My only idea is use string property and then convert it to XML Node (using XMLDocument and LoadFrom method).