Airliners do include provisions to help evacuate the passengers on the ground. Those provisions (quick opening hatches and slides) provide the basis for an idea that might possibly work on the Shuttle with a SpaceHab full of passengers, at least a better alternative than launching the unit out of the Shuttle cargo bay.

I'd look into incorporating a mechanism like explosive bolts to blow the Shuttle cargo doors in an emergency, followed by a hatch on the SpaceLab itself. You could then evacuate the SpaceHab using slides similar to those used on airliners. Of course, only the Shuttle Commander would be able to blow the cargo doors and SpaceHab hatch but that's just a detail. The real question is whether you could route the slide away from the likely flames.