It's his car. If he wants to slam and stance it let him. No rub. No love.
Tyre stretch is not the end of the world, and to those that choose to slam and poke a car they are well aware of the consequences. If we choose to still do it regardless that is our choice. I wouldn't go as far as a 215 on a 10" but honestly a bit of stretch is fine.
I know I am new on this board. But reading some of the comments a few guys make here and there really makes me cringe. Get off the "BMW high horse" and also the "performance car only". Just because you have coil overs it does not mean you are a performance guru. I track my other car with poke without a care in the world.