I've asked the same question in the past, and see it keep coming up. The lack of something centralised or coordinated for donations is a massive missed opportunity for FOSS.
This is exactly the sort of thing I think the FSF should take on. They are a nonprofit which exists to promote free software, and I think this should include the freedom to donate and receive funds. They are smart people and I'm sure they could figure out how to do it in an efficient way.
Thanks :)