1. I have enough experience in such games. Miner will work with your proxy, but it will cheat too, in several hours it will start to eat some shares, just 5-10% and it won't show anything about it. You can bypass detection of your proxy in miner in your new version but you will have to spend a lot of time to confirm that it works. And prove it to your customers. Since you have to have public "trial" version I will notice it and new version of miner will detect your miner again, and so on. Have fun
2. There are at least two other ways to disable dev fee, both are not too complex, so if some people really wants it I'm sure they have done it already without your "commercial software". Good luck in your business...