My TODO comments show up in nice view in GUI I use (Eclipse). I'm sure other GUIs have similar views somewhere. I'm also sure that plugin to turn old ones into syntax errors could be done in a day or two. That sound like much safer approach then runtime exception.
A day or two, really? That seems like an awfully long time requirement for what should be a simple change.
If you're experienced making Eclipse plugins, it would probably be under an hour. If you're not, it could take you a day to learn how.
I'm sure it is a simple change. The hard part is to find out where exactly should you do that simple change and how exactly should you do it. If you do not have experience with related APIs, you will need a day for googling and reading. Eclipse framework is huge and not all its parts are immediately understandable.
Use a decent editor.
Alternatively, you could continue using your editor of choice for editing and use grep to identify TODOs in your code.
Yes, if you're disciplined, and remember to do this regularly. But humans aren't perfect.