Your brother has a serious problem–and it's not simply the danger of losing his job. His real problem is that he has allowed alcohol to get him in its grip, and if he doesn't face this and deal with it, it will eventually destroy him.
This is why I urge you not to cover up for him any longer. Not only is it morally wrong for you to lie for him, but you're actually hurting your brother by covering up for him. As long as he can get you to do this, he will never be held accountable for his actions–and he will never seek the help he needs. Slowly but surely alcohol will rob him of his abilities, and the time to halt its downward spiral is now. As the Bible says, "In the end it bites like a snake and poisons like a viper" (Proverbs 23:32).
Talk with your pastor or family doctor or another trusted adviser about the resources that are available in your community to treat alcoholism. Then let your brother know that you love him and care what happens to him–and because you do, you will no longer cover for him, but will do all you can to help him overcome this problem.
Most of all, urge your brother to turn his problem–and his whole life–over to Jesus Christ. God loves him, and Christ wants to forgive him and fill his life with the peace he needs. And if you have never done so, open your own heart to Christ also.