In some cases, making a negative wage may already exist.
For example, many managers work very long days in order to cover all their responsibilities. As company's make cut backs to save money, many are not replacing workers when they leave the job. This just adds to the amount of work that must be covered by the manager.
If you were to tally up the hours worked by these managers and divide them by the monetary take home and there maybe times when this amount is negative.
You may be able to include almost any worker that is paid on salary. Especially if their line of work has demanded longer working hours.