I don't get it; you want to defraud your employer alleging that you have paid for an economy ticket whereas you in fact have used miles/points to redeem an award ticket in business class?

Anyway, one solution could be to purchase a economy ticket and get reimbursed for the ticket price and use miles/points to upgrade to business class? Maybe not the best way to use points/miles, but it at least solves the issue of getting reimbursed for ticket paid for.