Yeh I think it will be really difficult to find someone, especially as what one person see's as an Elvisy trait in someone, another might not.
I think through his daughters eyes this will be even harder. Dont envy her.
I think an impersonator who can act would be ideal, someone like Klush maybe. There are so many fantastic look a likes now days. And an ETA would know all about Elvis, down to his manorisms and how he moved etc - hopefully she goes down this route.