The honest answer for 3.3 Community Edition and earlier is that those two workflows are hard coded into Share. That said, you can still deploy custom advanced workflows to the core repository, but there would be work to do to integrate those into the Share interface. On the enterprise side, I know of at least one partner who has already done this sort of thing for their customer.
Another option by the way, is to use simple workflow based on a folder structure, such as "Drafts", "Pending", and "Published". This can be done via the content rule interface that's now in Share as of version 3.3 Community.
