Even though most Lexus dealers will say they can't be turned off, the DRL's can be turned off. The dealer needs to use their scan tool and access the menu where they can be turned off. I had it done for no charge on my previous 05, then 06 and my current 07 GX.
If the dealer says it can't be done, ask them to look it up in the Lexus service manual, it's in there.
Now some dealers will say that it is a safety issue and they will not defeat it. Then it's time to try another dealer. I always had the DRL's turned off before I took delivery of the vehicle.