[plt-scheme] Migration of planet packages across PLT upgrades

Is there a recommended way of "migrating" packages that have been
downloaded, i.e., PLaneT packages across PLT upgrades? Since I'm using
the default configuration, I find myself constantly having to
re-download all the packages that I need when I upgrade. My
~/.plt-scheme/planet/300/ has a multitude of directories.

Is there a migration system out there that can be suggested? Should I
setup symlinks prior to downloading PLaneT packages, e.g., 4.X.Y.Z =>
actual_directory/? Has this been discussed before?

-- 
Rommel M. Martinez
http://www.bespin.org/~ebzzry