Keyboards get supplied 5V, upto 500mA via USB. Most use in the neighborhood of 100mA. Now whether or not things on the keyboard leave it at 5V, or mess with it, is another story.
Long story short, get a multimeter, even if just a cheap one (Harbor freight was just giving them away a week or so ago), and test them. Without tapping into additional power or changing controllers though, I wouldn't bet on being successful.