Handling XML data Using WTX map

We have a WTX translation map from xml to Legacy format. The source xml type tree has been created with the XSD schema. Currently the map was working fine with the xml data because it is matching with type tree structure. However the client is saying now there might be a situation and possibility that their customers will send undefined xml xpaths (Refer Note1 below) in the xml file and the WTX map should not fail in this case. We known in general the map will fail because type tree structure miss mach with the xml file. Since the undefined xpaths are not been mapped/used further downstream to target Legacy systems and so we need to ignore them.
(FYI - Refer Note 2 below).
To make client happy and do not want to impact client business, we need a solution for the above mentioned.
Note1 - Elements not defined in the source type tree / xsd, also which is not known the place holder in the complex xml file.
Note2 - During map development, the xsd was used only to a create a input type tree because it contains huge structure definition. Here the map should not do a xsd schema validation and so we selected input card settings under document verification as well formed option. Another Option we selected direct xsd file in input card setting at type tree location and then selected document verification as well formed option.