Well, for what it's worth I'm in a similar situation -- whenever I have a little money in PayPal there are more urgent expenses. And the list of games I'd like to donate to just keeps growing. I don't see what Itch.io can do, either, other than help promote worthy games the way they already do, so that hopefully they'll be seen by more people with a disposable income.
As for what you can do, may I recommend making collections of the games you like and showing them off on your profile? Then you can point other people at them, and maybe some of them will have the money. Otherwise, it's just hard.