In my experience, since the world at large is ignorant of truth, revealing truth to them will always result in conviction; in this age, creating conviction in a person in the workplace can be considered an ethics issue and you could find yourself on the carpet in HR.
MY suggestion, as has been said, is to reveal portions of the gospel in your life, serving, mercies, etc. Build a lasting friendship with the person on typical grounds. If a person knows you, and you have invited them into your life, apart from sharing your faith, they will know u care. In time, you will have the opportunity eventually to share truth and exhibit a gospel caring, which is at the epicenter of why you truly care for the person; spiritually, as well as personally.