Create and claim password protected coupons as extension for the Burstcoin blockchain.
With the Burstcoin API you can first create and then sign a transaction locally, which keeps your password safe. Usually after signing you would broadcast the transaction immediately to enter it into the public memory pool of the nodes, so it can be included on the blockchain.
The model demonstrated here with BurstCoupon, delays the transaction broadcast by encrypting the signed transaction bytes with a arbitrary password. Turning it into a ‘coupon’. The recipient of the coupon will then need the password, to broadcast the transaction that is within it. The transaction now has a lock that can be controlled by a 3rd party without access to the senders wallet.