The explanation given by The Walrus is pretty much what I have previously heard quoted. I find it more believable than some mythical version of Cockney Rhyming Slang. I have NEVER heard the phrase Mickey Bliss and would reckon that is just something completely fabricated.
Mind you I come from "Up North" where Bradford non-rhyming slang goes "Apples and Pears"= a bag of fruit!
Quack!
GtD.