The way around this is so easy, and could be fun. If you were to go to PA to get fireworks, have a friend meet you in PA, somewhere near but too near where you are buying. You first go and purchase your fireworks. Drive away. Meet your friend. Put your purchases in HIS vehicle. Then you split up. Your friend drives back to NY a while later, and you head directly home, passing the fireworks place again. (or even going inside to "look around" but don't buy anything.) When you return to NY, they search your car, and find nothing. It screws with their heads and wastes their time.
Of course, this is just put out there for purposes of discussion. I wouldn't recommend breaking the law, you see.