What you're asking about is the concept of voluntary underemployment. Based on how long your wife has been working in this way, my guess is that you could spend a great deal of time and money on this and generate lots of animosity, all without enjoying any benefit in the way of reduced requirements of support from you.
If you're bound and determined, begin gathering classified ads for persons with her skills, specific examples, anecdotes from friends, and any other information you can showing that a person with her skills could work for a specified income. Gather it all in one place.
When you get ready to visit with your lawyer about all this, try to present the information in a cogent, concise way that persuades the lawyer you have a valid point. You're facing an uphill climb, but this will give you the best chance to succeed with it.
Lee Borden - Divorceinfo