When I'm reviewing multiple commit pull-requests and want to see everychange made, I always either click on the "Files Changed" tab on github,
which collapses every commit into a single diff, or do the equivalent
with git log.
Why doesn't that work for you?
One advantage of using github is that they're an independent thirdparty; we should think carefully about the risks of furthering the
impression that Bitcoin development is a closed process by moving the
code review it to a server that we control with explicit review groups.