That's an interesting point. I personally do not know either. My points of reference when it comes to minstrel shows are mostly derived from old time radio and records I've heard (Amos n Andy, certain Jack Benny episodes, Moran and Mack). In later films, you had Al Jolson singing 'Mammy' and Bing Crosby performing 'Abraham.' None the examples that come to my mind seem to have much to do with slapstick, with the exception perhaps of one character threatening another in certain cases. However, I would have to imagine that for all the years which minstrel shows were popular, there had to have been some acts which contained slapstick gags.