That's the thing... if takes away the joy of the game if you start a round and after a couple of holes your left on your own. Part of the fun is playing against others.
I do understand the point that disconnections are not always intentional. But if is disconnected 9 out of 10 games, he should either get a better internet connection or he's doing it deliberate.
My suggestion, if you don't want to give a penalty in strokes/stats, is to maintain an additional figure. Calculate the percentage of finished matches. And either make it visible so everyone can decide whom to play with, or make it an option in creating a group. For example, you only want people to join your match with 60% or better finished matches.
It's plain nonsense that nothing can be done.