To the best of my knowledge and if I understand your question correctly, there is no way to send a pre-constructed XML file or snippet with SOAP::Lite. You can however "hand roll" your SOAP::Lite packets by using the SOAP::Data and SOAP::Header objects. If you provide an example of the XML you wish to send, we may be able to help you build it.

Update: After reading the docs more closely, this may be what you are looking for: COMPOSING_MESSAGES_USING_RAW_XML