Ok, that's a tricky problem. The beer is already carbed, and likely a lot of the yeast has settled. Even if you wanted to jazz up the carbonation to make up for losses while transferring to 12 ouncers, you'd probably have to agitate the growlers to get the yeast evenly distributed before the transfer. And then you'd have to spitball just how much priming to use, without creating a bunch of grenades.
It all seems dicey to me. I'd be inclined to just call it a day, enjoy the growlers as is, and get your next brew going