I've often wondered this about the Alleluia. At the Cathedral of SLC they usually sing a second Alleluia verse due to the grand size of their sanctuary and the amount of time for the deacon to get the blessing, retrieve the Book of Gospels, and climb the high pulpit.

On the surface of it it would seem a harmless 'addition' to add verses when needed at the Alleluya responsory. However, it is sort of a regret to do this outside of Eastertide which, historically, has been the only time at which more than one alleluya was sung (at mass). Myself, I would be inclined to improvise during the preparatory ritual and time the singing of allelya to come to an end just as the procession reaches the ambo.

This is how we do it at Walsingham, where the gospel ritual is expanded to include a procession of crucifer, torches, thuribler, boat boy, book bearer, and deacon out into the first few pews of the nave. After the reading the improvisation resumes until all have returned to their choir stalls and the homilist has entered the raised pulpit outside the rood screen.

(And, there is this to consider: it is illicit to add to or subtract one iota from the ritual text. No one, high or low, has genuine authority to do this.)

So I should have looked more carefully.

For the traditional rite, the De ritibus servandis in cantu missae (1961) says clearly (para. I, VI, and IX) that additional verses from the same (idem) psalm, may be used if needed. In the case of the Offertory, chanted from the ancient (antiqui) Gregorian chants -- so this covers the case of Aristotle's transcription. The 1908 Graduale does not contain this permission, it seems. Also, there is no hint that this is allowed for the Alleluia or for the Tract, or anywhere else: and only for sung Masses.

For the new rite, in the Ordo cantus missae (eg in the 1974 Graduale) oddly this permission is not repeated -- it explains how to make processions shorter but not longer. However I cannot believe that additional psalm verses are forbidden, since what cantus could be more aptus?

I conclude: for processions, including the Offertory, where Psalm verses are sung, the current rubrics of both "forms" allow additional verses. But nowhere else, including not for the acclamation at the Gospel. For a longer Gospel procession I'll conduct slower or start later, to end at the right moment, as MJO suggests.

If you need your gospel acclamation (obviously OF) to be longer, I'd suggest either what MJO says, or you could choose something "crazy" with a total of 19 alleluias by the end of it.
http://www.hymnary.org/hymn/CP1998/page/842

What if you sang it in English, and then in Latin? (our St. Isaac Jogues missals always have the propers written in both English and Latin. So, it isn't exactly "odd" when we do an English chant, followed by the gregorian in Latin... though, we haven't done this for the alleluia.)

....followed by the English...

Just, um, curious - how do you sing 'alleluya' in English?
There are several kindred and loose translations - which one do you use?

Something like...

Well, "Yay, happy worship related exclamation" really goes with all these happy-clappy triple alleluyas that are heard in most of our churches, doesn't it. It even goes with the one quoted from no less than that of the Vatican choir at the top of this thread.

If people realised (as I'm sure many of our Forumites do!) that it really means something like 'praise be to Yahweh', or 'glory be to Yahweh', it might suddenly dawn upon them that these silly little song and dance jingles that are thoughtlessly gushed forth every Sunday were the embarrassment that they are. The last syllable of 'alleluya' (or its Latinate form, 'alleluia') is the first syllable of God's very Name, 'Ya'. An alleluya at mass certainly deserves far more gravitas and depth than most seem inclined to give to it. And, of course, this is the very reason that we sing it as the gospel is about to be proclaimed - 'Praise be to Yahweh!', 'Allelu-ya'. There is nothing, absolutely nothing that approaches the appropriate musical rendering of this mystical ejaculation of praise than the one single historic mass alleluya with its jubilus.