How to file 'nontaxable' income on your taxes, without...?

having to PAY IT BACK IN TAXES! Ok, so in box 14 on my w2 i am given a 'per diem'. I am paid weekly and the amt of per diem per week is NOT taxed. I was told by corp office that all I have to do is prove that I am using this 'per diem' for work related expenses. OK so of the $8880.00 I was given for the yr, I have $6812.00 in rcpts to prove was work related expense. SO why in box 1 on my w2 is showing this 'non taxable' amount (and in box 3, its not) and HOW do i file my taxes with out having to 'pay' ALL this 'per diem' money back in taxes.... b/c I dont have 'enough' expenses to file a Sch A?? PLEASE HELP ME UNDERSTAND THIS!