This gets asked every now and then, and I can't remember if there have been unofficial answers. There cannot be an official one.
I use the rules for Lord of the Rings figures, plus a few miscellaneous, so I just pick the rules as I see fit. There are a lot that line up, and I wing it otherwise. For example, I use stats for wild boar riders (or something like that) for my giant wolves. Wood elf druid on unicorn for the unicorn.