How long would you estimate it takes someone to "properly learn version control"? When I work with very junior developers they pick up git quite well in a week or two at most. Beyond that almost every team I work with uses their own special homegrown git workflow anyway.
I don't mean to put you down for you requirements but git is really really easy to learn. It would be a shame to miss out on a talented developer for something an otherwise well qualified developer could learn in a weekend.
I'd be very surprised if asking people to waste a week of vacation on only a 66% chance of getting a job (that they probably don't even need, if they're already employed) wasn't a strong filter against top performers.
> I tell people that the worst case scenario is that they use a week of vacation, but because of the extra pay they can take a nicer vacation later on.
I mean, how can they, if they've already used their vacation time?
I don't mean to put you down for you requirements but git is really really easy to learn. It would be a shame to miss out on a talented developer for something an otherwise well qualified developer could learn in a weekend.