Is it possible to use XStream with an abstract node?

Question

My client application is making calls to a service that returns a common "root" XML, but a different result node. The "root" XML contains possible error codes. Is it possible to use XStream in this scenario? Example:

public class RootNode {
    ErrorInfo errorInfo;
    BaseResult result; 
     ...
}

public class ErrorInfo {
    String message;
    ...
}

public abstract BaseResult { }

public class SearchResult extends BaseResult {
    List<Object> searchResults;
    ...
}

public class AccountResult extends BaseResult {
    String name;
    ...
}

The XML coming back could be one of two formats:

<root>
    <errorInfo><message>...</message></errorInfo>
    <result>
        <searchResults>...</searchResults>
    </result>
</root>

OR

<root>
    <errorInfo><message>...</message></errorInfo>
    <result>
         <name>...</name>
    </result>
</root>

I have set up my XStream object as follows:

XStream x = new XStream();
x.alias("root", Root.class);
x.alias("errorInfo", ErrorInfo.class);
x.alias("result", <SearchResult.class  OR  AccountResult.class depending on what I am expecting back>);

Of course, when I run this I receive an error telling me XStream cannot instantiate the base class (BaseResult). For fun, I also converted the BaseResult into an interface but received a similar error. I've looked through XStream's documentation and it isn't clear to me how to handle a situation like the one I just described. Is it even possible to do using XStream?

Thanks,

-Dan