Possessives

What is the appropriate way to form the possessive of a phrase? E.g., is it, "I'm going over to a friend of mine's house," or "I'm going over to a friend's of mine house." The second way sounds worse, but they both look odd.

I know, you could say, "I'm going to the house of a friend of mine," but that sounds way too stilted. Or you could say, "I'm going to a friend's house," but that seems like cheating.