The backing in Have A Nice Day during the choruses is of a similar structure to that of IML so it'd be interesting to take a look at some live footage of that song and see if they use a bt.

To be fair though, the backing vocals holding the notes in those songs during the choruses are pretty taxing so it's not a surprise that those would be bts purely because of the duration they are held rather than a lack of vocal range amongst the band.