Is There a Way to Do Fat Transfer on One Butt Cheek Without Going Under?

Fat may be a good modality to correct asymmetry of the buttocks.  This, of course, depends on your individual case.  The other thing with fat is that you usually need to place about 40% more than what you want to end up with, as that amount usually receeds after fat transfer.  Best to see your Board Certified Plastic Surgeon.  Together, you will come up with a plan.

I think it is possible for a small amount of fat to be transferred.  For buttocks it is usually a little more volume that is needed so a little anasthesia would be better for your pain and comfort

In short, yes. It depends on a number of different things, including how much additional fat you have, how well you tolerate procedures etc. But most fat transfer procedures can be performed under local anesthesia with some sedation and are well tolerated by patients. And, this can be done on one side alone relatively easily.

You should see a board-certified plastic surgeon in your area to get a formal opinion through and in-person consultation.

Best of luck!