A mix of laundry bleach and borax might work.  Or maybe just borax.  Leave them in a spot that gets a lot of direct sunlight and they should bleach pretty well(real primitive, lol!). On the other hand, I've never tried the borax.  I would guess the bones need to be pretty clean, though.  I will throw a couple into some borax mix this afternoon and see if it. Works.
Hawkdancer