I was reading a posh mag that i found on a train and there is a new-ish machine out that apparently "gets rid of hampster cheeks in a lunchbreak" I'm sorry i dunno the name of it and its probably mad expensive but i do understand your prob. I could look anorexic and i would still have chubby cheeks, i blame my dad.
It's all about light and shade - if you shade in the apple of your cheeks with a blusher slighty darker than your skin tone and in a matte finish (no shimmer) then use a highlighting blusher on your cheek bones this makes the face appear slimmer. Boots no 17 do lovely highlighting blushers in pink and peachy tones.
hth xx