Brain fart. Yes, if you boil the sugar/water and put it into a sanitized container you should be fine. I force carbonate kegs so I was forgetting the boil step of preparing priming sugar for bottle conditioning
The amount of sugar in a priming solution shouldn't come out of solution even if you freeze it. Worst case it might settle into water and sugar-water regions (like brackish water floating on seawater), but that would take a long time and simply stirring would redistribute things.