Hi there,
I think this topic might help you:
http://forums.gentoo.org/viewtopic-t-497125-highlight-updateworld.html

when you run it with --prepare option it produces a nice emergelist file
under .updateworld folder which you can easily edit, and when you run it
with --install option it will autoskip and resume failed packages and as a
bonus will provide you with the list of failed packages also.