Credits go to @Claire for the guide. This was originally made for just SMG as an answer to a question in their forum, expanded to include SMG2 as a guide for our Multi Mario space.

First, download the save file and extract it. Make sure you take out the .bin file. Then, go to the root of your SD card. Once there, you'll see a folder called "private". If you don't see that folder, than make a new one and name it private. Inside of that folder, make sure there's a folder called "wii". Once again, if there is none, then make one. Then, inside of THAT, there will be a folder called "title", and if there is none-- you guessed it-- make one. Inside of that, you want to make a folder named one of 4 things: If you're using the NTSC-U version (North American version), make the folder named "RMGE" ("SB4E" for SMG2) If you're using the NTSC-J version (Japanese), make the folder named "RMGJ" ("SB4J" for SMG2) If you're using the PAL version (European version), make the folder named "RMGP" ("SB4P" for SMG2) For the Korean version of SMG, make the folder named "RMGK". For the Chinese version of SMG2, make the folder named "SB4W".

Finally, move the save file (.bin) into that folder, and make sure the save file is named "data".

Then, put the SD card in your Wii/WiiU, go to the Wii menu, press the "Wii" button in the bottom left corner, press Save Data, go to the SD Card tab, and you'll see the SMG save. Just press that and click copy, and it'll be copied to your Wii save data and when you boot up the game, you'll have the file. Note that if you already have SMG/SMG2 save data from the same region on your Wii/WiiU, you have to delete it before copying the save from your SD card. When using the WiiU and homebrew to region-free load the game as VC, you may need to boot up the game after deleting the save to be able to copy the save over.

Note: You can find downloads to the save files on the SMG/SMG2 leaderboards or here on the Resources tab!