I think that it will be quite difficult to make this possible exclusively from individuals. Unless there were a threat that the projects will stop, or an offer of doing more that's pretty clear, most don't have a strong incentive to give. Something like kick starter helps to solve this in a way tipping doesn't. What about a sponsorship component? Facilitating companies sponsoring a programmer? Their github page gets…
The payoff for the sponsoring company will be the good reputation it gets from that developer ecosystem. There could even be a way to connect this sponsorship to recruiting developers from that ecosystem as employees (the bonus being that they are already familiar with this project)