You could just take a photo of the sculpture and paint it on your phone with a cheap editing app. You would just need to infer the shadow areas and paint them black, and the sunny parts white squares. QR codes were made to be very resilient to noise, and I can attest that you can mess with them quite a bit before they won't decipher. My boss asked me to take a QR code linking to our website and to try and rearrange some of the squares to be our initials. I got a few to work, and learned that the Reed Solomon encoding duplicates the data so much that this egregious manipulation was still acceptable.
Of course by doing this, you remove some of the error correction. Your mutated QR code is less likely to be scanned by a camera which is lo-res, at an angle, in dim light or affected by some other imperfection. People who test customised QR codes almost certainly only test them under close-to-perfect conditions.
My test conditions were transferring them to a black t-shirt with an iron-on printer sheet, and then taking a jpeg of my wife wearing it in the kitchen with an iphone and using a QR code recoder app.
