Extended form validation and blank fields

[eluser]urrmurrmur[/eluser]
I just read your reply in the bug reports forum, which states that it is impossible to call validation rules unless the field is defined as required.

Fair enough, but then my question becomes: I want several different validation rules, each testing if a field is blank, but each with a different error message. I could of course set the error message in each individual controller method, but that seems like overkill. So what I was trying to do was to create an extension to the form validation class with three or four self-defined methodes to test if a field is blank.

But as I understand it now, that's impossible? Any other suggestions on a clean way to do this?