Wolf, I don’t see the problem here. As you said you get a receipt in the mail from the organizations that you give to. Why not take a few minutes of your time when those receipts come back and give some thought to those particular organizations and what they are doing and what the people they are helping and you are helping need, and why you should continue helping them. Then mark them down on your list of organizations to include in your auto-pay program.
In that way you are involving yourself in the purpose of giving the tzedaka while doing it in the way that is most functional for you.