I used to be able to get a generator panel with Pushmatics in it. You would put a 2 pole in the first position (sub-feed from panel) then another 2 pole in the next position (generator feed). They were tied together with a plastic interlock piece that would allow only one breaker to be energized at any one time. You would add breakers in the other positions for the loads you wanted on emergency power. Pretty trick stuff...
