Use a different XML Serializer with ServiceStack web service

I'm trying to use ServiceStack (V3) to imitate an already established web service which communicates in XML.

Problem is... the XML format uses attributes, which are not supported by DataContractSerializer, but are supported by XmlSerializer.

Can someone point me in the right direction, how would I replace XmlSerializer with DataContractSerializer?

I could probably write the serializer (or adaptor, I've got the DataContractSerializer exmaple), but then using that serializer as some sort of plug-in? That is my question. Is it possible? I don't want to have to fork source code etc, just write my own class and plug it in.