I got system menu 4 working but WAD Manager gives me the ERROR (ret = -1) no matter what card I use. I even tried USB Storage and my SD Gecko and all 3 worked before. I have had trouble with wad manager 1.3 before, but even 1.21 is doing it
Oh also I don't think it'll be possible because the wii also needs the titleID installed for it to run anything from SD.
Though I guess you could get a batch program to make the encrpyted files for SD, and another program for wii that batch installs titleIDs for files made with the first program... it'd still be a lot of work to make.