I think this could be a good way:
Person A connects via TeamViewer on person B's computer with Bitcoin Core open.
He then sends X BTC to an address of his, enters the password (in visible mode) and OK.
If the password is correct, the transaction should be done.
Greetings.
EDIT: For added security, the first password entered does not have to be the real one, nor the second, nor the third... maybe the fifth.
EDIT: IMPROVED METHOD 2
Person A connects via TeamViewer on person B's computer with Bitcoin Core open.
He then sends X BTC to an address of his own and the rest to an address of person B, enters the password (IN HIDDEN MODE) and OK.