Cover, insert and duplex print job

So in our office we have a Kyocera 3552ci. I have to send out a mailing with an insert from other departments. Unfortunately they were pre-printed. So I have 2 stacks of paper and a 2 sided doc to print. I need them to end up collated 1,2,3 not as 3 separate stacks. I think it can be done with Cover and Insert each pulling from a different cassette/tray than my print job. I have been able to get 1 stack to go as a cover page and a duplex print but the insert won't print (I think because it is set to go in front of page 3 but there is no page 3). I have been able to get the cover and insert to

Question by Tristan on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.