If you're not feeling any fullness before the morning feeding, you shouldn't have any problem just skipping the morning nursing--assuming you haven't had any mastitis/plugged duct issues up to this point.
If you do experience some fullness or discomfort, pump just enough to relieve the pressure and place raw, cold cabbage leaves in your bra to diminish milk production.
Unless you want to go all natural...a couple of days of over the counter antihistamines can also dry up your supply.
It is fantastic that you've gone 18 months. My little one is down to naptime and nightime nursing--I have no doubt that she'll go at least until 18 months. I am just happy that I don't have to pummp at work anymore!