Search the database for monsters of level 70 or less. Given the HP, ATK, and drops, Velociraptors are probably the best bet, especially the ones in the third cave on Oslya.
Use equipment to lower your speed and raise the pet's, assuming you have a high level. Get them to match as closely as possible.
If you can use an attack that won't quite kill the raptor, then having a higher speed will ensure that when you don't combo, the pet gets the kill, which gives extra points (though not as much as a combo).
Then you need to just follow the advice of Ron Popeil, to "Set it, and forget it!"
Come back in a few days to see how things are going, but don't expect better than 1 level every day or two. This will go about as fast as leveling without bursting.
Oh! Give them a Belly Chain or other +350 HP item if you can.