I'm not sure if this is already possible but it may be a feature request.
Rather than using one of the template selection options when creating a blog (drop down, thumbnails etc), I'm wondering if I could pre-select the template for the user using a GET variable.
So I might have a Photo Gallery template and an Online Shop template. I'd have marketing pages for each of these describing their features, and I'd want the user to be able to sign up to either with one click from the marketing page.
So the user would be sent to e.g. mysite.com/register?templateid=12 where templateid is the id of the template I want to deploy to his new site. So he wouldn't see the other templates as a distraction when he goes to register, there might be dozens of others.