go on your ipod to ipod_control>device>sysinfo
and open the file in wordpad.
find this line of code:

buildID: 0x03028000 (3.0.2)
visibleBuildID: 0x03028000 (3.0.2)

change a number with a lower number

buildID: 0x03018000 (3.0.1)
visibleBuildID: 0x03018000 (3.0.1)

now the updater will think you have firmware version 3.0.1 and will let you update without restoring the entire thing.

this has been tested with 3g and 4g, the example above is 4g, the 3g uses different numbers but its virtually the some thing, just decrease the number. it should also work with other ipods but i’m not sure