There is a mod that is usually used for racing but it can also lower the load of the alternator to the engine. It's called an underdrive pulley. This is a replacement pulley or pulley set (depending on application) where the ratios are changed to make the engine "accessories" turn slower at idle.

"Accessories" would include the alternator, power steering pump, water pump. Typically the engine "gains" back around 5 to 10hp. If you are not into racing, this can translate to better FC numbers.

It is found on a typical car that the slower turning alternator is not a problem and the battery charges adequately during normal road driving. This assumes the electrical load is close to factory stock (no massive ICE installations) and the alternator is in good condition.