"Embedded" is what the reporters were called who traveled with the troops in Afghanistan and Iraq.  That situation is similar to the one Shimon described.  I used to work for a company that made interior/exterior truck washes.  These were large and complicated pieces of equipment so when we sold one we sent someone to work with the customer for a week or two to iron out bugs and to train the staff of the customer on its use.  We called this employer an "adviser."  This is also similar but not identical.