The whole point of this trinket is to save you mana. Popping off a few flashes of light is not going to be beneficial, since their huge mana cost is going to outweigh the benefit of getting the mana reduction sooner to the point that its not even funny. In fact, you should hardly ever be using flash of light. Go look at the holy pally article a while ago that talked about how much to cast what and such.

In addition, 1 point word of glories? No thanks. it may get you the mana reduction slightly faster, but its not taking advantage of the mana reduction. You could probably use one at the very beginning of the 20 seconds, but not later. because of the GCD, it only quickens spells (and therefore mana reduction accumulation) by a short time. this means that word of glory is only slightly more effective in terms of mana reduction accumulation than, say, Divine Light. When used at the beginning, the ability to get in another spell is going to be worthwhile, since you are only giving up a small amount of mana reduction on the word of glory to get in that last spell which will have more mana reduction.

(Remember, don't think in terms of "getting the mana reduction sooner", because what you're really doing is squeezing together your spells in order to fit in another, higher mana reduction spell at the end.)