any 3 products (from the category) for ￡6

Hi

I’m setting up a WooCommerce shop. The client has a product category of greeting card designs, all priced individually at ￡2.50 but wants to set up a discount for ‘any 3 products (from the category) for ￡6′.

I need to set the discount up so it applies to each multiple of 3 products.

ie. first 3 products for ￡6. 4th & 5th pricing at ￡2.50 each. 6th product will then be ￡6+￡6. etc.

Is this possible with this plugin? I’m having trouble finding a plugin that manages this.