According to :

As dangerous as this is, is this even possible?

Of course. 4 wire 240V is 4 wire 240V, and breakers don't care
which terminals are the innie and which are the outie ;-)

We were installing a new main panel, and just when we wanted
to transfer the feed, the local power company went on strike.
Out of necessity (because so much had been transferred to the
new panel), we ended up temporarily backfeeding the new main
panel thru its dryer circuit from the old main's dryer circuit.
[The new main didn't have a meter installed nor the main
feed of course.]

During the great ice storm, a friend and I helped a muncipality
out by doing inspections of generator installations. One of them
(installed by a professional electrician) wired the generator
directly into the panel's backplane (they were lucky, they
just got their power back, and all we did was remove the
backfeed and reestablish the real feed). The main breaker
was wired open.

During the same ice storm, we spliced a 100Kw generator directly
into a main panel (after physically disconnecting the line
feed). [This was at the municipal works garage, and became
a base for emergency crews, road clearance, and included the
army's food/fuel distribution center.]

In an emergency, you gotta do what you gotta do. However,
if you do have to do this, you have to do whatever you can
to make it safe (ie: wire or padlock or physically disconnect the
main). Secondly, if you are preparing for an emergency
_before_ the emergency takes place, do it right. Installing
outlets and obtaining a suicide cord is not right.

[Theoretically, an illegal backfeed can earn you a $6000 fine
here. Worse if you hurt someone.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.