You’ve got some pretty complete answers here, already. Keeping it short and simple, use your knowledge of biomechanics and have your client experiment with some of the same or familiar exercises done at different angles, perhaps with different grip/wrist positions. Keep the weight light to start off so that your client doesn’t strain too hard. Help your client to understand how body position throughout a range of motion can make all the difference.
The phrase “an inch makes a mile” has never been so true when it comes to form on any given exercise. By simply changing an angle on an exercise, you can increase/decrease load on specific muscles. Once you help your client to understand how to activate different muscles/muscle groups on command, it should be fairly simple to determine what will work best to get those target muscle groups working a little bit harder.
My advice is for you and your client to take some time and experiment with it. Make sure that whatever you and your client decide on is going to be safe and effective.