After years of this, I've just gone to changing the oil based on the Condition Based Service monitor. A couple years ago I ran 20k on the oil, the lab oil analysis came back clean, with plenty of mileage to spare. So I trust the computer and the oil quality sensor.
Plus, over 27.500km, I've essentially replaced half the oil thru consumption and some leakage- I've topped it off with 3 litres in total.
I can't get the oil filter cap off without the tool. I guess I could have my parents mail it.....but what difference does it make? I'm not driving the car much between now and 2. January; half the time it will be sitting at the airport car park anyway.