I don't get why you seem so set on knocking, it's just awkward. It won't convince anyone who isn't tipping to do so and it certainly might put a few who were off.
Door-knocking a bit brash no? Better off just dropping some 'subtle' cards in with the papers on his next round and seeing what comes back in the next couple of weeks?
As an aside did think back when I was doing this that a nice little earner at Christmas would be to get up before the paper...