That’s funny now that you mentioned I went to search in deep, and you’re right. There’s no way to donate to it at this moment. I thought they’ve added an option for that already.
However, it has been mentioned several times about adding such option (even I talked about it before), but I guess this is not their goal or won’t just go with their business model.
I’m not quite sure how the donations would go, but people also mentioned that hosting bounties on BountySource.com or something like that would be a great idea.
The employee Trey Greer said there’s the HackerOne project already, and even you talked about this, but bounties aren’t available yet. But maybe you’d like to check more sources and see if it’s needed to cast votes or discuss more about these ideas.
Oh, don’t forget to give it a shot on the Roadmap that’s pinned on the main page of FR.