Best that you don't put a slick at the front or rear. If you are determined to use a slick use it only at the rear. The square edged tire on the rear will make the mini handle weird but probably won't be too dangerous unless there are other problems with the stability of the bike. Under no circumstances should one be used on the front unless you only ride very slowly and don't care if it handles evilly. At higher speeds there will be a stability problem.
There is a reason that not one motorcycle in the known universe that came with anything but contoured tread.