Web Service Data Source Complex Parameters

I am building a report that takes a web service as data source. This web service does not take primitive types as parameters. The signature is something like this:

<soap:Body>
<GetXml xmlns="myreports.ws">
<root >
<TP Name="string">
<B Name="string" Surname="string">
<SA xsi:nil="true" />
</B>
<B Name="string" Surname="string">
<SA xsi:nil="true" />
</B>
</TP>
<TP Name="string">
<B Name="string" Surname="string">
<SA xsi:nil="true" />
</B>
<B Name="string" Surname="string">
<SA xsi:nil="true" />
</B>
</TP>
</root>
</GetXml>
</soap:Body>


My question is: how do I pass the xml to the web service from reporting services.

I have seen examples with simple types. They do it with this query:

<Query>
<SoapAction>myreports.ws/GetXml</SoapAction>
<Method Namespace="myreports.ws" Name="GetXml"></Method>
<Parameters>
<Parameter Name="Parameter1">
<DefaultValue>some value</DefaultValue>
</Parameter>
</Parameters>
<ElementPath IgnoreNamespaces="True">
GetXmlResponse{}/GetXmlResult{}/diffgram{}/NewDataSet/Element{@Attribute1,@Attribute2}
</ElementPath>
</Query>

But there are no example on using xml directly instead of parameters. Can anyone help me? Where do I put my xml?