Anyone know a good way to help them unionize if I don't actually work there?

I'm sorry to be a pessimist but winning NLRB elections and legal challenges isn't going to win Amazon workers anything. Amazon and other companies are realizing that they simply don't have to negotiate with the unions and there's nothing that anyone will do about it. Even many employers that have legacy bargaining units are refusing to bargain new contracts because they don't have to.

We are rapidly entering an era where worker militancy is the only way to win a contract and unless Amazon workers actually start doing that they will be shit out of luck.