Accessory feature for vehicles with push button start?

[Revved]

I know this should probably be in the wiring section but there is a better chance of getting a well rounded answer here...

I'm wiring a car with a push button start from a Ford GT and from reading the instructions on the kit pushing the button once turns on ignition, pressing and holding starts the engine... So what about accessory?

You get to your destination and are sitting in the car waiting with the engine off and you want to listen to the radio or roll the windows down...

I'm wiring the car with an ISIS system so it easy enough to wire a latching switch to turn on whatever circuits I want but it got me thinking...

How do you turn on accessory features in a production vehicle with a push button start? I know accessory delay will keep those functions on for 15min or so after shut down but what then? Push button start is fairly common nowadays in higher end vehicles so someone here has to be able to answer this.

Thanks