I solved it with a Java snippet:
// Your custom imports:
import com.saxonica.xqj.SaxonXQDataSource;
import javax.xml.xquery.XQException;
import javax.xml.xquery.XQResultSequence;
// Enter your code here:
try {
final XQResultSequence result = new SaxonXQDataSource().getConnection().prepareExpression(c_XQuery).executeQuery();
while (result.next()) out_XML = result.getItemAsString(null);
} catch (XQException e) {
throw new RuntimeException(e);
}