level 1 staff, run to Castle Zvahl Baileys in the past, hit the fortilace thingies or w/e til they die, gain lots of skillups!
Can do this while you sleep :P
Actually if you /NIN, the Ni spells can do some fairly decent damage (3k-4k range), and you could pair that with your WHM magic. Getting Staff Lv70 and getting Earth Crusher is the much better option though.