I take it that permanent workers have uniform (e.g. a coat) which is assigned to them? Just get some more coats in various sizes which aren't assigned to anyone. That way, you have the same standards for everyone. Make sure you order enough, e.g. if you have 7 coat changes available accounting for washing time available for each permanent member of staff and you have 10 temps, you need 70 coats. Don't be tempted to scrimp on it, the clothing is an important part of food safety.
If we run out or have a couple of fire evacuations so run out of normal coats, we do use disposable ones but they're not ideal and when you work out the cost of them, it's actually more economical to have laundered coats instead.