Congestion pricing isn't (supposed to be) punishment for driving a car when transit is available, it's designed to internalize the actual costs that driving a car imposes on others (i.e., takes up room on the road, among other things). So what you're suggesting is that cars should be subsidized in cities where transit is bad. But this doesn't make sense. If you are worried about a negative shock to the poor-ish, you should just give them cash.