1) Remove excess decor (heater, plants) in tank to reduce heat capacity of tank, making it easier to cool, more stuff = more heat to hold.
2) I''ve been thinking of having water from HOB flow along a metal channel/canal (aluminum?) with a small fan blowing across it, possibly with riparium plants in channel
3) A powerhead with emersed spraybar with fan blowing across.
4) Small portable room air conditioner, put tank on wheeled stand and refrigerate it in small room to conserve energy vs using a large room.
The only problem would be minimizing evaporation, and resulting hardening of water.