~snip~
This is basically the solution but it's kind of redundant.
A simpler one would be to just sign the tx that would spend all his coins right now. And store that transaction on a server. Write code in your favourite language that broadcasts the tx after Y amount of time just for an added layer of security. And open up a port on your server where the application can listen to.
If the application doesn't get pinged once every X months, weeks, whatever, then it calls the function, and after Y amount of time, the tx will be broadcasted.
So he has to ping the server every X interval, and if he somehow fucks up and forgets, he has Y more time to stop the application from broadcasting his coins.
Hell if you want I can probably set this up for you in node.js right now.
That's not really redundant.
Your solution involves trust. OP could theoretically broadcast the transaction earlier (e.g. working together with the recipient).
This should definitely be considered.
Heretik's solution on the other hand doesn't involve any trust.
The owner of the coins is the only one who can initiate that transaction (by not creating a new one).
IMO that's the best solution for a dead mans switch (at least the best i can think of).