I rely on spontaneity and momentum to get the words in my head without relying too much on mnemonics (since I want them to fade pretty much immediately). Basically, anything that I can't figure out based on Japanese words I already know, or through rote memorization, I spend a few seconds coming up with any kind of random wordplay + story, based on whatever useful context is at hand (the sentence itself, for example) or comes to mind (a scene from a movie or previous story, for example). It's a kind of rapidfire word association... 伝統的 becomes, in the course of a few seconds, 'traditional dental method of transmitting messages overall' and maybe think of Real Genius (old Val Kilmer comedy where they plant a mic in someone's teeth or something, I forget) or a paranoid conspiracy theorist.
That whole process is something I try not to think about too hard for reasons such as outlined by Jarvik7, it's just a few seconds to build extra pegs in the mind, and I rely on what Supermemo calls
planned redundancy as well as the successive layers of SRSing to make it stick (to make the word stick, not the spontaneous mnemonic, I seldom repeat one of those, though it's hard to say, since I forget them all). I've been learning around 35-70 words/day with this method, and frankly it's been a breeze. If you only do your cards one way, I could only recommend doing this with passive recognition cards, as I haven't found a need to test it yet with active recall (since I'm only doing single words as active recall).
Also, I find it less and less necessary to do this, the more Japanese words I know, since the audio and semantic associations are already there. I also tend to use Japanese words in the wordplay mnemonics as well, the ones I know well enough not to worry about 'interference'.
Random aside: I probably only would have spent a few months last year working on this method, but, among other things, I screwed up when I was trying to work some other aspects of my SRSing (incorporating all sensory modalities), but now that I worked that out, it's smooth sailing.
Edit: Forgot to mention, as yukamina points out, a lot of the aforementioned reinforcement stems from using frequency-based lists like iKnow/Kanji Odyssey.
Edited: 2009-02-06, 12:38 am