What can be done to improve a witch chin/chin ptosis without shaving/removing bone? (Photo)

In the frontal photos it does appear that you have a long chin so there is likely a bony component to your case. A profile photo and x-ray would help further delineate the problem. Without surgery, using Botox to the mentalis muscle might give you some improvement when you smile but reduction surgery (both bone and soft tissue) may be your best long term option. Another suggestion is to simply suspend the soft tissue pad of your chin in a superior direction thereby creating a deeper mentolabial fold. This can be done with a permanent suture and a tiny bone screw. Good luck . 

I understand why you want to avoid surgery on the bone. However, bone changes is the only way to change the shape of your chin. We can really change the muscles and how they contract. Chin surgery is safe if done correctly in expert hands.