The French Foreign Legion figured out how to do it. And they certainly aren't a 'soft' group.
The French Foreign Legion is extraordinarily selective in recruiting.
While the many, many 1000s of men from around the world showing up to apply annually are already self-selective as the kind of men any fighting unit would want, the Legion only accepts about 8 to 13% to try out for being the tiny number they accept.
You are incredibly mistaken to think they are desperate for bodies instead they are completely in the driver’s seat.