The Right Job
This is not possible in every job so find one in which you can get paid while you do nothing. Ideally be at least in mid level management and have some people who can work for you while they even do not realise it. Also, there should be little or no supervision on top of you to keep a check. A lazy or laid back boss will be even better.
Talk fast with coworkers and subordinates acting like you are really busy. See the watch a couple of times while you are in discussion with them and have a very serious and worried look on your face. Do drop hints that the job is tough and you are trying your best to meet the tough demands. They will certainly be impressed by your work ethics and efforts.
Just about every task in an office is very doable and not too difficult when you are a professional, though some can take very long. Pick up a small task and convert a ten minute job into an endeavour that requires hours of hard work. This will work particularly well if you are the go to man for this particular job. Take your time and act as if you are too busy.
Use Computer to Good Effect
Working on the computer makes you look busy. Even if you are playing solitaire, it appears that you are performing some important task and you are really busy. You can delegate “some parts” of the “important and urgent” task from your subordinates and while you act like you are working too hard, they can do your job. Compile the parts and submit the report without doing anything other than compiling and submitting it.