I would just keep him warm and not hibernate until he gets a little and a lot bigger. Older animals have more body fat and takes longer to burn it all off, so it's not as dangerous if the temperature is too warm and he is actually starving... I would just keep him inside in a shallow rubbermaid tub and use a 25 watt light bulb to keep him warm. That's what I'm doing with my yearling, too.

Here is a video of my yearling: