Any suggestions / hints for toning abs for those who have already had tummy tucks (witch hazel)?

Usual Exercises. You will find that the usual exercises helpful in toning the abdominal wall will be the same that will be useful after tummy tuck surgery. For example, the use of planks and standard situps should do the job. Careful attention to a balanced/healthy diet will also be important. Best wishes.
Core strengthening . Begin core strengthening with a mat pilates regimen progressing up to more agressive training programs with a cadillac or reformer. Yoga is excellent for overall health. Physical therapists may also assist you in the proper perfomance of these exercises and in good body mechanics for maintenance of the result.
Personal trainer. About after six weeks you can start going back to the gym. Get a personal trainer to focus on your abs. Start gently because it may be pulling on your deep sutures. Besides toning your abs, you also need to watch your diet, eat healthy and keep your weight down.
Surgeon's clearance. You do want to get your surgeon's ok before strength training to be sure that your abdomen is adequately healed. Then it is really a matter of the training that works for you. People tend to be different in that regard.