Sagittonius, you would probably get a better informed answer if you describe the particular circumstances you want to satisfy.
In our case MrsWigwam is the Motability customer and the primary driver (on a good day). I am a named driver and live with her. Our son is also a named driver and lives elsewhere. Our understanding is, MrsW and I live as a unit, so most of my driving is for her benefit. Our son only drives the car with MrsW on board and so for her benefit. I can’t think of circumstances where for him to use the car for himself would be for her benefit.
As I said, if you describe what you want to do, I’m sure people will chime in. Having said that, Motability are the arbiters and are very approachable.