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.
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.