DallasTitan:
I never did check to find if they made blank center caps, I know they don't make them with the Nissan logo. I had a spare centercap when I had this truck that I was going to experiment with, but I never did it.
I also have Infiniti Q45 wheels on my Murano and I got the blank centercaps for them. Although I didn't get the centercaps direct, I was told they come from
http://www.luxurywheel.com/ . I bought the Q45 wheels off of eBay and the came from a Sarasota Florida tire shop, the wheels were pakaged in a Luxury Wheel box and the sales guy told me that was where the centercaps came from.
Long story short, you can call them and they may have centercaps for the QX56 wheels also.