It's not quite so simple because what do you do if the POH authorises peak-EGT ("best economy") but the engine can't make peak EGT without excessive vibration?
Then you can fly either at the "best power" setting (which cannot itself be determined accurately), or at some unknown flow rate which is what you get if you lean "a little bit".
I don't think there is a solution, without decent instrumentation. You just have to be very conservative on fuel planning. A Shadin flowmeter costs about £3k. An EDM700 is something similar; costs only US$1200 to buy but the rest is UK disti markup and installation.