Poetry elements/sound devices include alliteration, assonance, consonance, and rhyme. An example of a clue would be "assonance 3" for "code", "control", and "candy". I checked the rules, and I’m unsure. This is the most relevant rule:
Your clue must be about the meaning of the
words. You can’t use your clue to talk about
the letters in a word or its position on the table.
Gland is not a valid clue for ENGLAND. You
can’t tie BUG, BED, and BOW together with
a clue like b: 3 nor with a clue like three: 3.
Unlike "b", "alliteration" actually lives up to its meaning as a hint that it’s similar consonants at the beginning of words. However, the words "code", "control", and "candy" don’t have anything to do with alliteration itself in the meaning. I suppose the line "You can’t use your clue to talk about the letters in the word" makes it illegal, but it’s fuzzy.