Wolf,
I certainly wouldn’t stop giving tzedaka online out of concern that it’s not helping you to develop your midda of kindness. Ultimately the point of tzedaka is the help it brings to a needy person or organization… otherwise there would be no point at all in giving, because it wouldn’t even be defined as a kind act.
One option is to put a pushke into your home or make sure to bring a quarter or dollar to shul on weekdays, and place a coin or dollar bill into it each day. That way you can afford to continue supporting your tzedaka online in a timely and regular manner (which really helps them with their budgeting) while at the same time train your hand to be giving. At the end of the month or year, a pretty good donation will have amassed in your pushke too!