Join a forum that allows you to have a link in the signature. Dig up old threads and post things like "I have this problem too, please help." Mods/Admins come around, see the dead thread resurected and close it. Once you have a bunch of old, closed threads with your posts in them, ad a spammy backlink to your signature and never go back. The signature backlink should be found by Google, but in a dead thread it's unlikely any person is going to see it. Viable?