Probably really incorrect, but if anyone could tell me what's wrong with this I'd be very thankful: "Das ist wie ich ihn vetreten habe"
It isn't really wrong but very clumsy.
Anyway, I think you're missing a comma in your translation. In my humble opinion it should be: Das ist, wie ich ihn vertreten habe.
How is it clumsy? Is it still clumsy with a comma before "wie"?
The comma doesn't add anything to the elegance. It's usually a bad idea to translate "that's how" to "Das ist, wie". (Although sometimes it works). It's just not very natural to put it that way in German. To me duo's solution sounds much better.
Interesting. Thanks for the heads up, wataya.
"Ich habe ihn so vertreten." was marked wrong. To be using "So" in this context, does it have to be the first word, or do I have the word order flipped somewhere else?
Your solution is correct.