A simple trick that does something similar without needing AppleScript is this:

1. create a playlist containing all the songs you would ever want on your iPod, name it "iPod Songs"
2. create a smart playlist named "Current iPod" with the following rules:
   • check: Match the following condition
   • Playlist is iPod Songs
   • check: Limit to 3500 MB selected by random
3. attach your iPod and open the iPod Preferences in iTunes
4. choose "Automatically update selected playlists only"
5. make sure that only the playlist "Current iPod" is checked
6. close the iPod Preferences and update your iPod

Now you will get a random 3.5 GB sample of only the songs that you want the iPod to have. To change what songs are shuffled onto your iPod just add songs to or remove songs from the "iPod Songs" playlist.