Great idea that would save having to clean the pages of the slate. I carry the primary plan on page one of the slate and the contigency/lost gas plans on the front and back of the other two leaves of the wrist slate.
3M General Purpose Vinyl Tape
The vinyl tape also comes off quite easily (afterwards) from both wrist slates as well as Wetnotes pages. Be sure to use VINYL tape and not just white duct tape. Even permanent marker will rub off the slick surface of the duct tape. (Though I have used duct tape covered by clear packing tape and that works as well.)