In my shop (magento 1.7.0.2) customers can order cardboard cutouts with a personalized design (by uploading their picture).
I want to implement a volume discount per uniquely customized product. For example: the customer orders 5 pieces of the product with his own picture A, and 1 piece of THE SAME product but with his own picture B => then the volume discount should apply only to the 5 pieces with picture A
(reasoning behind it is, as you probably guessed, that making one piece is expensive but making a duplicate is relatively cheap).
The products are simple products with a custom option (i.c. the uploaded picture file).
How can you create such a volume pricing?