Go to a stage you can clear in less than thirty seconds and equip everyone you use to do it with brokers. Repeatedly clear the stage for fast pulses of income.
The efficiency cap on Brokers is 300 per character, if you have more than 300 points in Brokers on a single character they will only earn 4 times the normal HL from kills, this is where the broker bonus caps. Brokers only generate bonus HL for kills, no other source of HL is increased by Brokers.
Defeat the highest level enemies you can, the HL reward for a single level x times 3 monster is more than for three level x monsters. (Killing a single enemy with a high level rewards less EXP than killing a handful of enemies with the same sum of levels.)
Steal high rank items with cheep hands.
Stage 9-4 Cross Point. Capture all the enemies here for roughly one million HL a cycle, between visits to Cross Point be sure to unequip all the orbs from the wraiths, sell the orbs you don't want to keep, delete the dead wraiths at the Dark Assembly, then visit the hospital, in that order.
With a 300 broker and a one shot against CoO3 sword your HL woes go away quickly... If you can't hack CoO3, try 9-1, Valgipus IV to warm up, and hit the item world to properly prepare.
I remember testing this, but I don't remember the outcome: steal HL from your allies, I think it actually increases your HL total, you need a high level ally to overcome the price of the stealing hand and a high level rogue type or Thursday to steal stats from so high a target, The stat that is available to be stolen is randomly rolled when a character spawns into the stage. So you can pop the target ally in and out of the base panel until the stat they have available to steal is HL.
Go to the item world, Steal! also set off every massive Geo Chain you can to get as many bonus gauge prizes as possible.
Speed Runners use massive amounts of good-for-nothing HP reduced casters, slaughter them all in the base panel by throwing a humanoid or too high a level monster into the base panel, clearing the stage then going to the hospital and selling the hospital prizes they don't want to keep, this exploit gets them above the designers HL curve early in the game.
I'm sure that somewhere in there is some advice that you can begin to use for HL farming.