I've known many district managers who preferred to offer the "outside hire" to PT supervisors. SO in most cases this works. It's not like the hard work will come as a shock, like it would with a true off the street hire.
Here's the thing though - with a 6:1 ratio, that ONE hire, mgmt can ABSOLUTELY hire whomever they want, because that's what the contract says.
So if you become a PT supervisor, and to use the term in another thread, then become a rooster about it, you'll be a PT sup forever. If you're a good PT sup, they'll take care of you 99% of the time, unless you have a management team that doesn't like you.
So, if you want to go the sure way, just put your name on the bid sheet and wait.