Not just a good idea this is actually done already by the blackhat guys, they also use the same technique to extort you in the classic "nice website rankings you have here, be a shame if anything happened to them" manner.
The disavowal tool really isn't that hard to use. Yes, it is more work than no work, but if you depend on a search engine for traffic, you're going to have to do some work to optimize for it (like, sign up for webmaster tools).
