Well, I got Showcase savegame injection working. Just extract your save with SaveGameManagerGX, point my utility at GDATA, MDATA, or RDATA (for games, comics/mangas, and records respectively), inject/extract/delete what you want, and install it back with SaveGameManagerGX. Note: Showcase will yell at you for "corrupted" files since I couldn't figure out checksums. Just select OK, it will only display it the first time the modified save is used. Nothing will be deleted, and your modifications should've stuck. Yes you have to have a softmodded Wii to use this.
Actually, you do not need a Wii soft modded to do so.
You just need a Dolphin emulator on your computer.
Steps:
1.Copy the save data of WWDIY showcase from Wii to SD card
2.Plug your SD card into your computer and use Dolphin's inject save data function.(Browse for sd:/private/wii/title/WA4E/data.bin)
*WA4E could also be WA4P or WA4J depending on the game's region*
*BE SURE TO MAKE A COPY OF YOUR CLEAN sd:/private/wii/title/WA4E/data.bin IN CASE SOMETHING GOES WRONG!!*
3.Browse for Dolphin Emulator/Wii/title/00010001/57413445/data for GDATA, MDATA, and RDATA, then edit them.
(The above works for US version, 57413445 could be 5741344a or 57413450 if game was JAP or PAL,
not confirmed though)
THANKS FOR HELP FROM leseratte, it has been know that the 8-digit numbers are actually
4 Hex ASCII numbers
Check them out here: http://www.asciitable.com
4.Extract all of your save data with Dolphin.
5.Check the directory of your Dolphin.exe, and you should see a folder named'private.'
6.Browse for private/wii/title/WA4E/data.bin then copy it right over SD:/private/wii/title/WA4E/data.bin
*WA4E could also be WA4P or WA4J depending on the game's region*
7.Plug your SD card back into your Wii, delete the save data for WWDIY on your console
(MAKE SURE YOU HAVE A BACKUP IN CASE SOMETHING SCREWS UP!)
Copy the WWDIY save from the SD card to your Wii
8. Enjoy!
Plus: You can get a WAD of WWDIY showcase to show off you games on a PC!
(The region of the WAD must match that of your save data!)
Edit: Some data do get corrupted. The Hi scores of DIY games were gone, and I somehow can't inject games into the 1st slot on Wii save(Record&Comic not tested)