I can't believe no one was able to help out with an answer or pointer on this one (or maybe I'm just not patient enough), but thankfully I was able to find the answer while reading through some other answers here on SO - unfortunately I can't reference the Question here, since I lost the page.
Anyway, this will do it:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *screenCaptureLocationString = [[defaults persistentDomainForName:@"com.apple.screencapture"] valueForKey:@"location"];
Amazingly hard to find this info for some reason, but hopefully posting it here will help someone else.