Perhaps Daneos you could try to dominate the auction house for a week or two with items like upgrade stones for an affordable price.
You could dominate for example the sale of upgrade stones by putting 20 U60-U70 upgrade stones in AH every few hours for an affordable price.
This way you will collect zeni, people will lose interest in farming for the items and eventually you will have collected a high percentage of the zeni that is in the game THUS INCREASING THE VALUE OF ZENI.
I'm very well aware of the negatives here, but if Daneos does this for a short period of time like say, 1-2 weeks then zeni will have increased in value, prices will drop and the amount of zeni in game will have dropped drastically.
(TLTR; Daneos takes zeni from the game by dominating Auction House so that zeni value increases and prices drop)