Can I 'unmatch' a rule programmatically in treetop?

Question

Is it possibe to skip a rule by validating it using ruby code in treetop?

Say there is something like this:

rule short_words
  [a-z]+ {
    def method1
      text_value
    end
    ...
  }

end

And I want the words size to be from 2 to 5 letters. Can I exit rule if I find that the length of text_value is not between 2 and 5?