Advice for people living in more than one country for iTunes and App Stores?

I know that we're unusual, but not that unusual, so hopefully there's some good advice out there.

I am Australian, my wife is Finnish, but we work in Papua New Guinea. That means that we spend significant periods in each of the countries, sometimes all three in the one year, like this year. Apple wants me to change to the store for each country, which is somewhat painful. Worse, I can no longer purchase anything in PNG, since I don't have a bank account or credit card here, and my Australian card is rejected (though it was accepted in Finland).

What is the advice for this sort of situation? Do I have to keep swapping stores?