Without purchasing a newer model iPod (your 2G canonly go to iOS 4.2.1)
Your only way is if you have the version that was compatible on your computer such as in the recycle bin/trash or in a computer file backup. In that case delete the current version that is in your iTunes App library and replace it with the older version. Then sync.
Also see: Recover Older Versions of iPhone Apps After Updating — Apple News, Tips and Reviews