You would have to say it, otherwise it would give rise to the possibility that it would be a constitutional amendment. Indeed, that is what the provisions were in the fixed date election law that was enacted in 2008. The law said there shall be an election on a certain date in 2009, but nothing in that requirement limited the powers of the Governor General, which therefore meant that the Prime Minister could, notwithstanding that law, go to the Governor General prior to that and seek an election. That has now been upheld by the Federal Court of Appeal as valid. Therefore, on this proposition the law would say the Prime Minister may not seek prorogation, but if he does, it's okay. So I'm not sure what such a law would accomplish.
On June 10th, 2010. See this statement in context.