Hmm...that's a tough one. I have a "muffins that taste like donuts" recipe and it has a dash of nutmeg in it. Also, sometimes cake donuts have a slight citrus flavor or like the princess emulsion flavor, just a tiny but, not a lot.
I might go with a specific type-- jelly donut or cinnamon sugar donut or boston cream donut --instead of a generic donut. I guess that doesn't really address the coffee part though... Sorry.