I certainly don't think it's needed. If the department wanted to deny disclosure, they would deny it. It would go to the commissioner, who would mediate it. That's what happens in Ontario, where the commissioner has the binding power. The mediators work out frivolous and vexatious requests, because the person is not requesting anything that is there or available, and they get things done in a couple of months in most cases.
Also, if you have an information management system that uses the Internet for the purpose the Internet works best for, which is to search for documents, and you proactively disclose and upload documents to the Internet, then you say to the requester, “It's there. Go and search for it yourself.” The way to solve this is proactively, not by creating another loophole. We need to close loopholes, not create new ones.