I am not sure if ripple is available to do Lock Time transactions? I find this to be the easiest way as you make transaction to other party you trust with your coins in it lets say you put it for next year. When date is coming close you simply pick your stash of coins and move it to another address before lock time transaction triggers itself so you go and make another one. I found this to be the effective way to ensure your money is not lost. It is sad to see that people haven't though about this because as we know everybody can die tomorrow unexpectedly.