I’m a big proponent of “positive reinforcement!” So applaud your client’s efforts for at least making the time in their schedule to meet with you. I’ve worked with some very busy clients (e.g. an eye surgeon, the CEO of a HMO etc.) and what I found that works is that once they begin to see results (feel better physically and mentally, see cosmetic results, feel stronger etc.) their self-motivation to keep the progress going may be enough to get them to do some things on their own.
By acknowledging their success in meeting with you on a regular basis, you give them encouragement, and encouragement will hopefully lead to self-motivation.
I hope this helps.