So you need to copy your bush, and then place it on your current bush. Then you set the alpha to 0.5 for the copied bush make a zone over the bush. Make it transmit entered bush 1 when you enter the zone and left bush when exiting. Then have your original bush hide when receiving on entered bush 1 and show on left bush. You can copy the hay bales and the zone as much as you want as long as you change the entered bush channel and update the hay bale to show on that channel.