I read in this question that to tame a Natural Beast creature that one must first calm, then tame, then train. Also, that this is achieved through an "extended" challenge. Is this true? And, if so, how does an "extended" challenge work? How is it performed?
I can't seem to find anything specifically about taming beasts with a Nature Skill Check. However, after some research here is what I can offer you.
First, a definition of Extended Skill Challenge:
Extended Skill Challenge- Multiple skill checks made over a period of time. To be successful you need to pass x checks before failing y checks. For example I made an extended skill challenge for a wizard to tame a magical lightning crystal in my game, he needed to succeed 5 checks before failing 3.
Second, while I cannot find this ritual on the online character generator* I found a link to a ritual that could be used to tame beasts aptly named "Tame Beasts". It is likely a homebrew ritual.
Either of these options should work for you. You can customize the extended challenge how ever you want. To make them harder you can raise the DC to succeed, increase the number of successes vs failures, or both!
*The character generator I speak of is from my subscription to D&D Insider that compiles ALL published rules/options for characters.