You might think about embedding bounties in crypto blockchains. For example, create BTC wallets that can be unlocked using a secret sitting next to (or steganographically embedded in) the secret you're trying to protect. This gives the person uncovering the secret an incentive to activate the canary. {RI,MP}AA are apparently doing this with their music and movies, so they know when they are showing up on pirate sites…
Check out https://medium.com/@grantm/obtaining-instant-breach-transpar... for some more info about how this might be possible.