Bakery variable shipping based on number of items?

[CodeALot]

My client wants to sell items in a webshop that are always of the same dimensions and weight.
He has determined that up to 6 items, the shipping costs will be € 4,- for the package.
Above 6 items, a different packaging is needed and the weight exceeds the limit for the cheaper rate

So what he wants now, is to have the webshop look at the number of items in the cart:
1 to 6 items? -> Shipping € 4,-
6 or more? -> Shipping € 7,50
 
As far as I know, Bakery can't do this. Would it be easy to implement this, and if so, in which file(s)?