The Workout Builder is a great tool for this. I also use Skype to interact with my clients if they have questions or need a demo. I would recommend you meet with the client in person before deigning a routine for assessment to see were they are and if they can execute the move with correct form.
You would design the program the same as you would if you were performing live one on one training. I’m not sure if you are a IDEA member but they have a workout builder that allows you to design and share workouts with your clients, and you can view videos of the exercises. There are other organizations who provide workout builders such PTonThenet.com. You can also use technology such as Skype to demo the training program.
Hope this helps!