You should be able to... but
not with Lexus' help.
I asked the dealer and called customer service at the 800 number, getting the same answer - NO
I can't imagine it would be that big a deal... the display is already there... and so's the wiring, apparently, you would need the camera and an electronics module. Acura offers a backup camera as a dealer accessory, if you have the nav display - makes you wonder why Lexus doesn't.