'Social proof''? It's a term Professor Robert Cialdini uses to describe the persuasive power of knowing that other people are doing it too. (Cialdini worked undercover to discover what really works in sales.)
Examples of social proof in action
Ever been at an intersection and crossed on the end of a red 'don't cross' light because other people were doing it? Me too. We were victims of social proof.
I was once in a queue leaving a tourist boat in Paris. As each passenger passed the tips box, a bell would ring to acknowledge another donation. Would you feel the pressure to keep the bell ringing? Everyone else is leaving a tip. The bell kept up its steady rythm.
Could you use the social proof principle in a less manipulative way?
How about showing how well the changes you're proposing worked out? Say, a similar company's experience with your product.
Maybe you could describe what happened when another team in your organisation adopted the new software, encouraged some people to work from home or changed to hotdesks. Your senior management team would want to know that.
Make a feature of your social proof - not just a testimonial, but a before-and-after story.