Fifth, keep a journal. I've never been a consistent journal writer. Yet, I found that journaling on vacation helped me to focus less on my work and more upon my life, not to mention my relationship with God. My journal entries described the events of the day, my thoughts and feelings, my likes and dislikes. Sometimes I would draw maps of hikes I had taken. Sometimes I would record a favorite restaurant and what I liked on the menu. In my journal, I would often write out my prayers, which helped me to focus more consistently on the Lord. I usually wrote out specific prayers of thanksgiving, which enabled me to savor life more richly.
Honestly, some of my journal entries would include brief notes about ideas I had for preaching. If, for example, I had thought of some sermon illustration, by jotting it down I could let go of it mentally and emotionally. Yes, I know that I was working. But writing in my journal enabled me to stop thinking about work related items rather than keeping them in some uncooperative part of my consciousness.
Sixth, ask for God's help. If you agree with my observation that pastors need to take an occasional break from pastoring, then why not ask God to help you? When you dig down into what's motivating you to keep on working during your vacation, you'll often find that you have a hard time trusting God to take care of things in your absence. You fear that if you stop thinking about preaching, your preaching just won't be as good. So why not talk to the Lord about this and ask him to help you trust him more. Perhaps you'll discover that God wants to give you the gift of a genuine, refreshing vacation.