Follow this guide. A 50+ year old casual Wii owner could do it when I showed it to him.
* Save files you copy will need to use the same trick to be copied back. System menu 4.3 disables this trick.
What You Need
* SD card
*
This folder
*
This file
* System menu 4.2
How to Use
1. Put your SD card in your PC. If it has a "private" folder, rename it to something else. (ex. "private-old")
2. Put boot.dol on the root of the SD card. (not in any folders)
3. Put the new "private" folder on your SD card.
4. Put the SD card in the Wii.
5. Eject any discs from the Wii DVD drive.
6. Start the Wii.
7. Go to the SD card menu.
8. "Load boot?" - Yes
9. Menu should reboot.
10. Go to data management
11. You can now copy any save file. The "copy" button will be grayed out, but you can still press it and have it work.
12. Don't forget to get your SD card back to the way it was if you changed it. (New save files will be in :/private, the hack will be in :/private/wii/title/aktn/, old folder will be whatever you renamed it to)