About the only way I can think of doing this is to try and exploit the accuracy limitations that all
electronic electricity meters have.
Most modern electronic electricity meters are Class 1 meters which have a variety of accuracy specs
depending on how much energy they have measured.
A modern utility meter is Class 1 with a very tight requirement to be accurate to +/- 1% down to 5% of load.
If the Meter has a maximum current rating of 100 A, then the meter will be accurate within 1% down to
50 ma , so anything below this means that the meters accuracy is not defined.
If the supply voltage is 240 V , then a load of less than 12 watts will be below the meters minimum accuracy standard
and whilst the meter may measure this amount of power, you could most likley argue that the reading is not accurate.
Running a 10 mw led of such a meter would most likley not be recorded at all.