Merging blogs

I have two blogs. How do I merge select posts on the fly? For example, if I have one blog about money and one blog about cars and I write a post about GM in my money blog, how do I merge it to the car blog so that clicking on the title directs you to the post on the money blog? An example is Wonkette. If you see a post with highlighted blue tags, it’s actually an entry that has been merged from some other blog.