Keep in mind that legislation that has a general impact on the public doesn't lead to individual conflicts of interest. For example, you might be able to argue that the Minister of Finance has a conflict of interest when bringing down tax legislation, but because taxes affect everyone, including the Minister of Finance, there's no real conflict of interest there. I think most legislation that the Prime Minister would deal with would have that general application, affecting the Prime Minister's assets only incidentally.
I just don't think that there would be recusal very often. I would guess a couple of times a year at the most.