It's come up a few times in the past and there's no current method. A while back, hte blue bar along the top only pointed back to the main blog, and then they added in the drop down menus for just the blog listings while the "New Post" link went only back to the main blog. I think the new drop down menus we recently got is sort of a work around for the time being.
Now, there are two things you can change that will affect some settings. You can edit your URL here in the forums under the View Your Profile -> Edit link at the top of this page. You can also edit your profile on any of your blog backend and edit your link there at Dashboard -> Users -> Your Profile -> Website. That will change the link underneith your name when you do sych things as make comments and the like. (Did for mine)
That's probably as close as we're going to get for your request currently.
Hope this helps,