yum downloadonly for different boot partitions?

I have 4 different flavors of fedora on my system,
with f8 x86_64 in use 99.9% of the time, but f8 i386
and f7 x86_64 and i386 available for testing
(which I sometimes need to do).

I was just wondering if some magical combination
of set-arch and chroot and the yum downloadonly plugin
could be used to get all the appropriate updates
downloaded for my non-active partitions, so the next
time I happen to boot, I could run yum update and
it would find it already downloaded the updates it
needs, so all it would need to do is install them.