You might be able to get a free license if you contact the developer and agree to write up a review on your blog/facebook. Rovio is a decent sized company (as far as mobile apps go), so they may be less inclined to agree to this. Smaller developers, will sometimes agree to do this.
Why don’t you want to support the development? It seems kind of ridiculous that you’d be willing to steal people’s hard work. Have you ever been robbed? How did that make you feel? A lot of these developers are just making ends-meet and could be making a lot more writing banking software, or customer management tools for big companies, but instead want to make cool things for people to enjoy. When you steal from them, you often end up crushing their dreams and forcing them to go back into a cubicle where their soul is slowly siphoned away into the corporate void. It’s worth a few bucks to keep that from happening.