I googled for
apple genius install windows and easily found this:
https://discussions.apple.com/thread/4995602
Ask them. We don't know what your local Apple Store will do for you. It will certainly cost you their hourly charge for however many hours are involved. You may have to purchase Win8 from them but if not you must have a copy of your own.
When my mom installed new software (not Windows) on her MacBook a few years ago, I suggested she ask the local Apple Store. As it turns out, she also asked a local repair shop who'd done some prior work for her on getting her wifi network up. The local repair shop was willing to do the install for free, and they were closer, so she went there.
In general, I recommend asking the vendor you intend to visit. I don't think there's a universal policy among Apple Stores, and even if there is, you might be a good enough customer that they'll do it for lower cost (like my mom being a customer of the local shop).