The thing with freelance instructing is, you still need pretty much all the things a Part 141 school would need when it comes down to it - aircraft, maintenance, fuel, premises, training aids, record keeping, instructor rating renewals, so bar an AOC and some manuals you wouldn't really have to go that much further to get a Part 141 approval, would you?
If you're teaching someone in their own aircraft, different story, but flying schools can do that too. I reckon you could set up a small Part 141 school for not much more than you would have to fork out to do independent instructing, or perhaps I'm deluding myself.