Wow, how surprising!
Recipes sometimes actually work better when you follow them!
Pulled the rest of the passionfruit ganache out of the freezer today to chocolate-coat. And, amazingly, it worked easily. Instead of melting and mixing with the chocolate, the properly frozen ganache worked like a charm :)
So, a lesson to all. When something tells you it needs to freeze for a certain amount of time - it probably does :)