The only luck I have had with this is to set the roaming agressiveness on the client device to be high. This way as signal gets weak, it will try to associate with a new AP quicker. Realistically though its hit and miss. I have a school where on one floor I can walk from one end of the building to another traversing 5 AP's and I might drop 10 pings (4 minute brisk walk from one end to the other). Normally even things like a file copy will work, but will stall a bit.