You didn't. :o
Of course Boris hasn't done as much as he should have - none of us ever do.
My point is that Boris should - and hopefully will - appeal to progressives much more than Ken on so many issues.
Boris introduced the London living wage. Boris argued for an amnesty for illegal immigrants. Boris will get the best deal for London transport infrastructure - why would the coalition do anything for Red Ken? Boris is arguing far more persuasively for protecting the London spending settlement than Ken, whose only line is "Tory cuts". And of course, it is Boris who introduced the Boris bikes!
Of course, Boris prefers freezing council tax and increasing fares. Ken would prefer the other way round. Boris wants to scrap the 50% top tax rate, Ken wants an 80% top tax rate. Boris stands up for the City of London; Ken wants to shut it down. Boris is very definitely a Tory but no-one can argue that he isn't in the centre of the centre. Ken is far, far, far to the left.