I agree with TX. Paying a salaried person "
overtime" can lead to questions like, "Why don't I get
overtime every time I work extra hours on a project?" If you feel that someone has gone above and beyond the call of duty to help your organization then give them a bonus. This way you can say it is for just that - a bonus for a job well done and going the extra mile to help the organization do X (fill in the blank - win a contract, get a deal, complete a project on time and under budget, etc.)