I have had this problem in the past. There is only one way to stop tankering, and that is to present an economic case. Yours will be to prove to the airlines that they are getting delays because of it. Delays cost big money and a few delays due tankering and it will stop.
My case was easy. They used to tanker on B734. I found out by trial and error that the max fuel on landing to avoid top wing icing was about 3500kgs. The saving into here was around 10GBP/ton, and the deicing cost was around 500GBP/occasion. They soon stopped.
All talk of the environment falls on deaf ears, only money talks.
With other aircraft you can use the centre tank. Big problem on A330 as there isn't one! On A319 I transfer fuel into the centre tank after arrival, putting about 3000kgs in the centre and leaving only 100kgs in each wing. This works well, and I have a long turnround to do it.