How to set transactions take 0 fee and no income for mining in private network?

[ssbg2]

Hi,
I came from Japan,Please forgive me for my bad English...
I have a private Ethereum blockchain,I don't want transaction fee whenever a transaction is posted in this private ethereum blockchain and I also want there is no benefit for miner,Because this conflicts with the company's business logic.
But I couldn't find any solution in stackoverflow and other forums which I know.Is it only possible to solve the problem by modify go-ethereum source?
Any help is appreciated.