I have a 16 page document with a sheet size of 9x12, it's a spiral bound so bindery would like slip sheets inserted in between every collated set. Not a problem as I have used the slip function before but not at the 9x12 page size. I don't see a custom page size where I can create this within the slip sheet size selection. This has to be a simple thing to do but as I have not done this before it's new to me. Anyone?