OK. If you're considering this in the context of novice users, I would say, please don't do this. The error you get is going to be misleading:
Too many arguments for Thing::hack at ./proto-method line 16, near "1)
Execution of ./proto-method aborted due to compilation errors.
If your goal is to help novice users, this seems to me not to be the a good idea, as the error says nothing about the actual problem. I don't think that this idea will help anyone, except in the sense that calling the method as a function will fail, unless they pass it no args.
Sorry. I've got no alternative suggestion, but I don't like this idea.