It's true mostly people who miss two turns are not key players, but sometimes they are..
I'm playing game 6020660 where the situation is that the player who is now kicked out has Europe, well defended (29 armies on it), this makes it for 'weaker' players unconquerable and for the strongest player (who has Africa) a gift to a lousy win, he doesn't have to protect that border anymore and can use all those armies to kick our butt

So it suddenly got totally out of balance!
Now hitting a magic button to get back in is indeed impossible, wouldn't be good for the game.. I'd rather suggest something like:
- when you miss a turn your 'deserved armies' (minus..%) are randomely spread over your fields..
- when you miss a turn your 'deserved armies' (minus..%) are randomely spread over your fields with the most armies on already..
- you can miss 4 rounds but then you're deffinately gone..