As a member of management, I would say at this juncture, you need to evaluate your relationship with your management. If it is good, tell them what is up and arrange the days. If you worked for me, I would give you grief for trying the back door week lock in, which wound up bringing a HUGE headache to my front door that I will have to spend hours meeting with the pissed of employee, my manager, the steward, you, your buddy that tried to "hold" your week, and others. All of which for no more money. Thanks a lot pal. Then I would wish you the best of luck and schedule you off for that week, seeing as I have plenty of staffing.
If you do not have a reliable relationship with your management team, you could probably try the call in method without being terminated. Though you might piss off your management team and make yourself, um how should I put it, under closer observation and training for a while. Especially if a few days that week layoff people refuse to come in to cover your route, no one can be found, and a management person has to run it. Which of course will be grieved and they will have to pay someone to sit home.
Now, to those of you encouraging this "sick" call in when he is not sick and advising him on what terminology to use and what UPS can and cannot ask him when he does - I want to hear no more moralizing from you about management only doing what is best for themseves and ignoring the letter and intent of the contract.