when reviewing a PR with only a few files changed, I simply create a local branch and c&p the changes (*cough, pretty sure there's a better way, but then that's the most simple ;).
With changes to many files (like f.i. https://github.com/openjdk/jfx/pull/569) that still would be doable, but rather cumbersome - so looking for something like "gh pr checkout 569" (not that I ever tried that, just copied from the doc :) inside Eclipse.
An alternative might be to fork-the-fork .. ? -- Jeanette
