use policy of the GnuPG-card

[Robert J. Hansen]

> One problem comes obviously in mind: Someone with priv access to your workstation,

You just lost.  Everything after this sentence is irrelevant.  Once an
attacker has privileged access to your machine it's all over.

> How is this supposed to be managed?

It can't be.  GnuPG is only for use in environments where you trust the
admins.  GnuPG cannot protect you from a rogue admin.  Do not fall into
the trap of thinking you can manage this: you cannot.