The thing is, you want everyone to play it to the end, so the only logical answer is to have all the loot at the end and not at any of the mid-bosses.

Ideally, the loot system could be improved in a way where the loot rolls can be changed (eg, "I would like this item, but not if this other item drops") based on what order you "need" on them. So you need on the items you want the most, greed on the rest, and the items are doled out in the order of most "needs" , then most "greeds"