I think the only way to pay above average wages is to expect above average productivity.
So a job that normally pays $8 an hour is increased to $16, that means one person has to do the work of two. That also means one less person get hired as well.
My brother is a restaurant fixer. He tells me that most restaurant operators schedule twice the amount of people for a shift then they need. Why you may ask? Because so many people do not show for their shift. That's what happens with those low wage jobs, you get people not very much into their jobs. Restaurants also have very low productivity, even though some people are working very hard. Its just the nature of that business. That's why the robots will take over some types of them no matter what happens with the $15 an hour thing. It has to happen.
And if you do pay an above average wage, you don't advertise it. In fact you don't tell new hires either. Because they aren't going to get that above average wage at first. You have a probationary period to weed out the folks that aren't going to work out, or are unworthy. The employees past the probationary period are prohibited from telling newbies the deal. The losers come and then go. Those that work out get a surprise when you become permanent. We work you hard, yup, but here you go, your worth it, you get a big raise. Now keep your mouth closed about it.
I think it would help current employees keep the freeloaders out, as they know the more of them there are, the harder it becomes, because of the lower staffing. Probably easier to get a 16 dollar an hour employee to show up then a $8 dollar one too.