I was thinking of a “feature” on manuals that ran electrical and accessory-belt stuff full blast during engine braking.

The best time to run your a/c or turn the seat warmers: when you’re trying to expel energy.

Would give you some extra braking without heating up the engine and take a small load off your brakes.

That or turn any vehicle into a mild plug-in hybrid for all electrical loads and flywheel the alternator until that time. Gasoline-powered generators are not very efficient.

Might get a few percent extra efficiency without having to touch anything mechanical.