Ahh, same boat, 27 inch iMac and all. Dunno about the translucent keyboard on screen. But, I have noticed some learn-touch-type apps in the Mac App Store. Plan on trying one or more out this weekend. One is free, Typist, and seems to have decent ratings.
Let me know how you make out, please. This is one of those things that's been on my todo list for ages, but with the relatively new iMac, I really need to get moving on this one!