Get ink removing carpet cleaner or the best carpect cleaner (has to be liquid) and use some comet. Mix them up and let each key soak for awhile. WARNING- I dont really know what going to happen to the letters. Make sure you wash the keys with the solution. Dont just let it sit there. It wont drift off. Add different things such as grease cleaner or that crap. If you get lucky, you might just find some ink remover.
You can try and use nail polish remover on the keyboards to see if this will work. You can dub remover on a piece of cotton and then rub it on the keyboards. Another option is using rubbing alcohol with cotton wool to clean the keyboard.