Philipp,
Java adapter module will be an overkill.
I suggest configure the scenario end to end as normal scenario. Test it, will fail with error "MalformedByteSequenceException: Invalid byte 2 of 2-byte UTF-8 sequence" (if you are using ICO) OR with error "BaseRuntimeException: Content is not allowed in prolog" (if you are using sender and receiver agreement).
Then remove the SWCV of sender interface in configuration. Test it again.
FYI. If non XML payload enters SAP PI / PO, these errors are thrown. It is because of new SAP code (secure - to avoid XML virus threats).