The next time your premium is about to run out, pick the premium buildings you like best and send them to yourself.
When the premium runs out, accept the contracts. If this works, the building should now be a non-premium one.
Extra Thought: You should probably have at least one open slot (so it doesn't see the contract and think you're buying while full. Ideally you should be below the 60 cap.
Obligatory Statement: Coins cost the same now that they did last year: 10 per Euro.
