Adaptive defrost is a field of research in itself. You can use what you have right now, no need for any external blower to mess with your results, but you'll have to adapt your strategy over time. Your fridge is a functioning balanced environment in itself. You just need to learn how to power it efficiently. Keep in mind that Temperature Regulation is a VERY SLOW process. First, you need the temperature inside your fridge at all time, that you can study at any time, maybe a sample every 10 sec. would be manageable? Try it to find out. You need to note the actions that the fridge performs (compressor on, compressor off), and mix with that your visual observations on the coil (amount of frost, thickness). The result doesn't need to be perfect the first try, but you need to try different strategies (power duration and rest duration) to find out which strategy work best for YOUR fridge.

Well, that's how I would do it! Good luck! Keep us informed about your progress. It's always fun and motivating to see good results out there.