I need to set a custom free-shipping threshold(in config this is
carriers/freeshipping/free_shipping_subtotal and can be set in the back-end) for each quote subtotal.
So to quotes above this subtotal amount free shipping will be applied.
The subtotal-amount will change dynamically(by user) and should revert to default value set in back end when user is logged off.
How do I go about doing this?