Hey Diogon! Wow congratulations on getting (almost) ALL the endings. <3 I'm hoping/guessing that means you are really loving DSG-R!
Ok sooo I can't quite recall *how* to get Coach. But I'll do my best (it's been a very long time).
I recall that you should aim for Polar (for the most part), but get the number of his towel wrong. Then you must go to the Charity Football Game, and Marlain should tell you about Polar's past. Afterwards, there *might* be an option to leave the field or stay, choose to stay. And then you'll get Coach. :)