Different unit and price for shopper groups

[sandomatyas]

There is a shop where customers can buy products and they have to pay every single piece. But they want to create a wholesale shopper group where the selected customers can buy these products only per kg. You can't set a static piece/kg ratio.
Like there are screws, bolts small plastic products in a hardware store. Of course there is a price per piece for the standard customers and price per kg for wholesale customers.

Is it possible to do somehow?