Oh sweet, I only need 1 lvl 81-100 pokemon in my party? And I didnt know Absol held Life Orbs :0 thanks!
I'm gonna stop you there :| While you
can get Leftovers with only 1 lvl 81-100 Pokemon, the odds are really annoyingly small. Since Pickup activates after battles, it's a good idea to get a
couple of Diggersby (or whatever) via GTS before you start farming, and equip them with Lucky Egg until they get to Leftovers stage. Back in XY I was using two level 90+ Diggersby and it still took four days for one Leftovers >:O The more Pickuppers (Pickers-up?) you have, the easier it'll be! And experience is relatively easy to get anyway so getting them to a high level isn't too hard. You can do it at the same time, even.
(Also, Absol only holds Life Orbs when identified via Dex Nav, so Compoundeyes farming won't work.)