Shipping options

I have a question surronding shipping options - I have setup shipping zones which is great. However where I am from in New Zealand - we have rural delivery, where someone lives outside of a usual servicable zone by a courier. Therefore an additional fee is charged (typically $3.50). 

Is it possible to add a check box "Rural delivery charge" and people tick this box if they live in a rural area? People know if they are a rural address.

Alternatively - are there any other ways to capture this rural additional cost? It's not possible in the shipping zones on offer. I am currently eating the additional shipping fee myself.

Thanks