I dont see a way round the problem the OP has tbh...
Really anyone who is skilled has a good reputation and does not quit unless they "call a loss" (acceptance of defeat).
So why take a risk with a stranger...
Then again , How can u ask this stranger to leave because your friends might never come so in the end you might need him to fill in the numbers...
The way I see it it boils down to that common creed "Lifes unfair" .
It is unfair , but one way to make it less unfair is to learn and become skilled , play everyday and gain a good reputation. Then people will know you want you in their games.
Its funny but this is how communities grow. Noobs who strive to get better because theres reputation targets to reach. I remmeber I played TA for 5 years just to get into a good clan for reputation.