The time has come to take shadow IT seriously and address the issue in a way that is inclusive to employees and meets the needs of the business.
Offer Alternatives
When an IT request is made, just saying 'no' doesn't help. If the business side requires a tool to get the job done, and IT doesn't make anything available, then they will circumvent IT. And it's likely management would side with business goals over security. To keep everyone happy and safe, it's best to always offer legitimate alternatives.