I just moved from WI. 🙂 I can help you with this. For K, it is not a required grade, so don’t even worry about it this year. Compulsory age is 6, or 1st grade usually. You do not have to show anyone either, so you will be fine. Use church/sunday school time as religion class, do what some of the others suggested (nature study is anytime you’re outdoors, or PE class, etc). You will easily rack up those hours. Even a K’er in half days (remember most are half-days for grade K, so that hour requirement does not apply – and again, it’s not a required grade-level, so they don’t even need to know you’re hs’ing yet) can rack up that many hours. When you’re ready for 1st grade next year, you will have so much practice getting those hours, you will barely notice when you pass it long before the last day of your schoolyear. 
ETA: Forgot to mention, you can also use chores, etc as “home ec” class. Cooking, folding clothes, picking up, cleaning, gardening, learning to sew, etc – all of that I used as home ec. You can REALLY rack up those hours quickly by counting these types of things! LOL Piano lessons are music class. Don’t think you have to get those 875 hours just from those 6 core subjects they make you teach (again, in 1st-12th). I hope all this is helping!