Can we have the Number of Days on an expense item default to NULL rather than 1?

Summary:

Is it possible to force employee to enter Number of Days for expense item? Currently default to 1 which satisfies the requirement without employee actually editing/confirming this.

Content:

The Number of Days field defaults to 1, which is causing inefficiencies in our Expense audit process. We flag all reports that have hotel charges with daily amounts over $500. Because the Days field defaults to 1 always, employees often do not touch it and will enter the full expense amount (or it will default in from a corporate card charge). Very often, an employee will enter a full week's hotel stay recorded to one night, which triggers the report to be reviewed unnecessarily. We are looking for a way to force employees to