Notating dipthongs in lyrics?

[padmavyuha]

Hello there - this is not a Sibelius so much as a general music notation query, but since I'm going to be writing it in Sibelius this seemed the best place to ask.

I'm setting a poem to SATB voices, and I want to make deliberate use of the dipthongs in the poem - i.e. in the word 'sky', for instance, there are two syllables, skah-ee, and I want to be specific in my lyrics notation that on a change of note, the voice changes to the 2nd syllable. Is there an accepted way of notating this, or will I have to make one up?

In my experience, choirmasters tend to get their singers to avoid 'thin' 2nd syllables like this, only sounding them as they come off the word at the end of the note(s), so I want to make it unambiguous that the 2nd syllable gets sounded for the full length of a note (or more).

If there isn't an accepted notation method for this, I'll have to go with phonetic lyrics, as in skah - ee for sky (or put a performance note at the bottom of the score), but I'd like to avoid that.