Here is a delayed one, a hint.
Actually, the answer is given in insert_hdr_any.png image file from faq_axis_adapter.zip attachment (note 1039369 - FAQ XI Axis Adapter) on a bit complex way. Let's imagine a situation where the values don't need to be dynamically read. Configuration would be as follows:
Processing Sequence
3 | AF_Adapters/axis/HandlerBean | Local Enterprise Bean | hdr
Module Configuration
hdr | handler.type | com.sap.aii.axis.soap.HeaderInsertionHandler
hdr | value.1 | <m:AuthInfo xmlns:m="urn:test"><m:usr>user</m:usr><m:pwd>123</m:pwd></m:AuthInfo>
Perfectly simple 