You should use Marketo's preheader feature in Email Editor 2.0. If you do, view as webpage comes after the preheader you've set.
I dunno. We've never used the view as webpage feature.
You could hard-code it in after the pre-header, and then paste the link in manually, maybe? I imagine that would probably mess up your click tracking within the view-as-web-page web page, though.