Mileage reimbursement

Hi, I travel often on business trips and I would like tro track the mileage reimbursement my company gives me. The simplest way to do this could be if I could enter a "negative" cost (currently not possible), or it would be even better if a specific action could be selected for Mileage Reimbursement (i.e. with km + reimbursement rate ). Any ideas/suggestions?

Manuel