Alrighty, fairly simple.
Introduce "boss encounters". These bosses would be a random encounter out of (I'm just gonna go with half the super ratio here for example) 1/55k fights. These "boss encounters" would require skill to defeat thereby earning the player the item (which would have a 100% drop ratio once you've managed to defeat that unique boss).
An example of how it could go:
You begin training, training, training... normal monster, normal monster...
*Pop up*
"You have encountered a boss(or insert original/unoriginal name here

), will you fight it?"
(You click "Yes")
*Battle begins*
Here is where the "unique" coding of the boss comes in, very much like when you ask an NPC for a duel.
*You manage to defeat it*
"Boss" has dropped a *boss's item*, where would you like to put it?
example: "Diablo has dropped a Diablo's Hammer, where would you like to put it?"
(You click on the slot)
(You do a little dance as this is your first weapon stronger then a lvl 8 )
Now 3 things come to mind for me with this:
1. The player should not have the defeat counted as a death and should not be given a death penalty. (Debatable I think, but I agree with this)
2. The pop up at the start of the fight is very important!
3. There's an issue here with the power of a "Diablo's Hammer" where Diablo might be a boss you can encounter in Noslin and a Llirrem super. Should the Llirrem be stronger? Personally, I think the boss weapons should be balanced according to the map they are found in just as a super is. So yes, I do believe the Diablo's Hammer should be stronger then a hammer of Lirrem but that's me.
There's plenty more details I'm sure (bring them up!) but what do you think?