If someone is paying you to write code, they have some say in the contract about how it is licensed. You could be upfront about only doing GPL, and they could be upfront about saying no. But if you try to do it after the fact, that's a violation of the contract.
Canines have five digits on their front paws, just like we do. Their "dew claw" is equivalent to our thumb, so the outside digit is still a pinky digit.