do you mean like a by pass ?
I have a 4040 , with a needle valve on the waste, just before it where it leaves the housing I have a t peice that by passes the needle valve with a ball lever valve on it, it then rejoins the waste pipe after the needle valve with another t peice.
When I turn on the water the tds is high so I open the ball lever valve on the by pass ( this diverts all water to waste )
Once the tds drops to normal levels after a few mins , I close it and start to produce pure. This also means that once the needle valve is set to the optimum waste/pure ratio there is never any need to adjust it when you need to flush the membrane.