Is there a way to see how much fat is in the buccal fat pad prior to surgery?

There might be some ways to determine the buccal fat volume with an expensive MRI scan or something like that. However, the volume is typically in the 2 to 3 cc range. This procedure is a subtle one, but one that can make an appreciable difference in the cheek contour. If you consider that we often use only 1 cc of filler to augment the cheek bones, removing 2-3 cc of fat can make a big difference.

The size (amount ) of buccal fat removal on a patient depends on the patient's anatomy. Some patients have very large buccal fat removals, some people have very small ones. The majority have medium size fat pads. The only way to know the size of the buccal fat removal could be with a head MRI, but very unlikely medical insurance will cover nor a patient will pay the cost out of pocket. Therefore is the plastic surgeon during surgery who can asses the size of the buccal fat pad. 

This would need an in-person evaluation, because it can vary. Buccal fat excision is an appropriate surgical procedure for patients that of overly full and wide cheek areas. In common terms, it is good for patients who have chipmunk cheeks. You are a patient that would need an in person consultation for a complete evaluation and explanation of the positives and negatives of these procedures in your situation.
I hope this helps.