Why couldn't it be just another boot-screen option, like the way Windows shows "press F8 for advanced troubleshooting options" when it starts to boot?
Puppy's boot screen might look something like:
Or something like that.In 10 seconds Puppy Linux will load automatically with previously stored settings. (Press "Enter" to skip the wait);
Press 2 to load Puppy Linux without using the hard drive (Puppy will need to be configured);
Press 9 for Puppy Linux to stop after each step of the booting process and wait until you press "Enter" before proceeding to the next step.