Though that ceratinly is a method used in many direction controlled converters.
If he/she knows and controls the protocol (master-slave)... Then to get the very best results he/she simply changes the direction before he/she transmits then change it back again shortly after he/she finishes.
OK, but the OP is talking about Rx/Tx pins only. No pin to control the RS485 driver. So he/she is changing the direction how? By using a port pin, yes. But he does not want that, he wants it with Rx/Tx pins only :)
So here comes the light sensor or the microphone :)