Already in use in RPC (at least in Java) – ‘Stub’ – which is the class that gets exposed but it’s not the’real’ thing.

From software testing (and other things), ‘dummy’ as in ‘dummy Objects’ which are the ones ‘filling in’ for the real ones.

‘pseudo’ is typically used as a prefix but it can be used on it’s own means false or fake, as in pseudo-science (not’really’ science) or an amoeba has a pseudopod (false appendage).