A thermal process is the only validated kill step for cocoa. The only one. Heat + time + steam (optional). "Organically compatible agent" is dubious - it may be effective, but i seriously doubt it. Sterilization means you've rendered every living thing dead. Living things are organic. Which means anything that is compatible with organic material isn't going to result in the sterilization of said organic material.
UV lamps will not be effective, as they're contact based -and with as many cracks and crevices as are found in nibs, you're going to have a huge percentage of your surface area that never is exposed to UV energy. Gas based sterilization agents such as ethylene oxide may work, but have not been validated.
Thermal processing is the *only* validated kill step for cocoa.
Strength is the capacity to break a chocolate bar into four pieces with your bare hands - and then eat just one of the pieces.