Electric motors are definitely one way to achieve this but it seems so crude to use a device that’s detectable after the race.

Instead, how about sealing up the downtube and filling it with a weakly exothermic gas producing mixture* and then adding some turbine blades — sorry I mean “triple butted crank stiffeners”, your honour — to the bottom bracket instead? One doesn’t normally pedal at 10,000 RPM so some other sort of gas-energy harvester design would be better but you get the idea.

In a similar way to the case of the [spoiler alert] man stabbed with an icicle, the evidence will neatly and literally evaporate into thin air**.

*Something on the chemical spectrum between “science fair volcano” and “sugar and fertilizer oh whoops I’ve made a pipe bomb” ought to do it.

**Erm, apart from the gas turbine bit.