Well, but the pending merges are just forked repos themselves, or do I misunderstand something about github?

I think you could go and add git remote refs. to those repositories and branches that represent the pending merges. For example, my change here is in 

https://github.com/libopencm3/libopencm3-examples.git

If you add that, you can then merge/cherry-pick/rebase from there. Same with all the other pull requests, as far as I can see. It would be nice, however,  if there would be a way to do this more easily, like a script that imports all merge requests for a given project as a bunch of remote refs. I couldn't find anything like that with a quick google. I found this, though:

http://stackoverflow.com/questions/6022302/pull-requests-from-other-forks-into-my-fork