technicallly, anything you can bolt on the motor..... so turbo's and superchargers can be bolted on.... if you have to go INSIDE the motor, you're bolting in, not on.....
i don't think that the amount of time dedicated to installation should be the defining element to what is and is not a "bolt on." i with the aid of one man installed a supercharger system from scratch on two different cars in the course of a workday.