How to stop expense report submission for the entire organization?

Hi,

I am looking for an easy way to stop new expense report creation in the system as part of our PeopleSoft Upgrade cut-over. Has anyone tried and tested such thing in your organization?

As part of the cut-over a communication will be sent out to employees to submit and approve the expense reports before a certain date before the cut-over start date. But since it is a large organization I expense the employees will still try to submit expense report which will hamper the cut-over activities in 9.2. Wanted a systematic way to stop it without modifying the employee profile or user security.