[CentOS] forcing yum to download but not install

Hey folks,

Is there any way to fake a "yum update" just to get yum to force a download
of all the files it needs, without actually installing them.

I finally have a RPM cache/proxy working and I just want to populate it.
The server I want to actually update cannot be updated until tomorrow but
I'd like to do a fake update just to force the RPMs into my cache so they
will all be pre-downloaded.

I don't see anyway from the man page to do this.

thanks,
-Alan

-- 
“Don't eat anything you've ever seen advertised on TV”
         - Michael Pollan, author of "In Defense of Food"