i never injected anything becuase i dont have any VC sadly but its basicaly like this
On your wiiu just go to the bowser you first need to run a kernel exploit(wich can faill i always get race attack like 2 or 3 times lol)
Go to fix home page he has all exploits hosted there
http://fix94.no-ip.org/wiiu
choose kernel(osdriver) if it exited the bowser then it worked if not try again
once your back on wiiu menu again go back to the bowser again and same link except now you choose codehandler option it will again exit back to the menu.
now open up your VC title pause the vc game to see the VC options and such, now on the pc hit connect on the gecko app you can use fix link to get the app of course on the app you need to put your wiiu ip and such before hitting connect.
if it connected well go to memory viewer right click upload data and you need the adress posted for snes VC injection afew pages ago and just hit upload, once its all uploaded on the VC menu on the wiiu just click reset rom or game or whatever that option is called and if it works it will work if not well it can simply blackscreen or crash your wiiu.
Also one thing you need to know you can inject a rom bigger than the original one becuase it will break the emulator so depending on the VC game you have your choices are limited what game do you have?