Have to agree with the majority - the coach isn't representing the ECB and isn't in charge of the game.
As someone who plays at a level where oppo team's players are regularly Umpires, this does happen, but I wouldn't say its the norm, in my experiences. If anything, some lbws we've appealed for have been optimistic and been given. There are some occasions that you feel are favouritism, but as a team we've always knuckled down, bowled and fielded well and made it very difficult for decisions not to be given. I wouldn't feel comfortable throwing a game and that would make it less enjoyable for me, even more so than having a decision go against us.
I think if you can walk off the field knowing you've given your all in the spirit of the game then your conscience is clear, as an individual and a team. Let them square it with themselves and justify their own actions, knowing you've played the game as you wish to see it played. That said, nothing wrong with telling the non-walker exactly what you think of him in the middle though! I would certainly be directing my feelings of injustice at him rather than the Ump or non striker - "I bet your parents are very proud", "that's 8 lives left - can I get you a saucer of milk?" etc...