predownload gnome packages for emerge?

I want to install Gentoo, is there any possible way of downloading all the packages for gnome (gdm etc) so that when I do an emerge it immediately starts to compile? What I want to try to do is download the necessary files, dump them in the portage folder then do an update of the files in that folder and then do an emerge for gnome. I don't have an internet connection and can't leave my pc where I'm going to do the install becuase the dl and compile of gnome is going to take some time I want to try and do it this way. Is this possible and if it is, how?

Does emerge with -f do what you need? if not then the portage info here may help.

It's possible. Man is your friend!!!

man emerge

The directory /usr/portage/distfiles is gentoo's storage for source files and all downloads.