I don't believe there's any way to set up customized error messages, especially since I think of admin console as being supposed to give you access to all products, not just workfront.
This doesn't answer your question, but for most of the companies I've been in, the support/IT team has KBA (knowledge base articles) that point any workfront-related questions to a point of contact within the company who is more knowledgeable than the IT team would be (in this case, it would instruct them to direct all questions on workfront to you).