I'm going to take a stab at this since I'm looking for something similar that I don't think exists. However, in your case, across the top are the pages of your blog. You most certainly could make a PAGE and put the link to your primary website on that page - saying something like "visit my apron store here" or whatever.
You can also add you primary site to your blogroll or create a banner for the site and put it in a text box on the sidebar.
At the moment it would be great to just have them close the blog and be redirected to the site. THAT'S what I'd like to see happen.... but I have yet to find any solution to the problem LOL!
If there are other thoughts and/or strategies out there, I'll be watching your discussion :)