Well there is a tool, called sfs resize, however, it only did partly work for me, because my 1Gb Partition which should have been splitted into to 512 mb ones, could be only resized to 700something mb (although just 300something where use).
But there is another solution (if you have enough space that is) I backuped my whole sys partiton with Diavolo Backup, splitted the old Sys Partition and formated both then. backup on the first, Mos 2 on the second one, everything was fine. But as I said, this will just work if you have enough space. (Or maybe sfs resize will do it for you, but please consult the docs!)