The only way to gain cheek fat is to gain all over body fat. That is probably not the answer you want to hear. When I gain weight, my cheeks fill up & my cheekbones look more defined, as a result of the increase in facial fat. I get a bit more projection on my face.
You can always have facial fillers injected into your cheeks to plump up the area. A lot of people do that these days. Both men & women have it done. The best filler that looks natural, is your own collagen or fat they take from somewhere else in your body. Hyaluronic acid also works well & looks natural in the cheek area. I have that in my lips & it looks really smooth. It looks natural under the skin & will last quite a while. Other facial fillers can look bumpy & lumpy under fluorescent lighting.