In the wiki example, 8 8 5 6 8, the 6 was ok because whilst "dispose" is 2 syllables it is read quickly to keep the beat: "to dispose of the rat".
To make your second line sound right, I would have to read either "whowere" or "werefull", like they were one word and it's just not intuitive to do that, so the beat is lost.
Poetry should be musical but the sound is from the beat (and the syllables and vowels), so it is very important to get the beat right.