Unfortunately you are asking for the impossible. You can
not be on a workgroup and Domaine at the same time. They
are both very different entities and can not coinside.
Why do you wish to do this? Are you dealing with a laptop
that uses a corporate network as well as a workgroup at
home. Or was this just a misunderstanding as to how a
network works? The only way to do what you ask is to use
hardware profiles. Set up two profiles one to access the
company network and one to access the home network.