[ic] Free Shipping and Shipping.asc file

[Sheamus Nulty]

I'm setting up free shipping for certain products we are selling and I'm
running into problems. My first shipping method "usshipping" is based on
price. So I have created a usertag that will calculate the total shipping
price for my basket while removing items that have been marked as Free
Shipping. So I put the following in my shipping.asc file

usshipping    US Standard    [shipping-subtotal]    0    0    0.00
usshipping    US Standard    [shipping-subtotal]    0    200    8.00

and so on.

However, when I have a shipping subtotal of 0.00 i.e. items in basket will
ship free, then this will just return an error on the checkout page
indicating that it can't find a method for usshipping. The shipping cost is
set to 0.00

If I change my usertag to always return at least a value of 1.00 and modify
my shipping.asc file as follows

usshipping    US Standard    [shipping-subtotal]    1    1    0.00
usshipping    US Standard    [shipping-subtotal]    1    200    8.00

then the error no longer appears but the shipping method isn't displayed.
Again the shipping cost is 0.00

If I make one final modifiaction to the shipping.asc as follows

usshipping    US Standard    [shipping-subtotal]    1    1    1.00
usshipping    US Standard    [shipping-subtotal]    1    200    8.00

then everything works but my shipping cost is of course 1.00 .

Is there a way to circumvent Interchange from thinking that a subtotal of
zero means it should report an error and when the shipping cost is zero it
should still return the shipping method. I'm currently using 4.7.5

Regards

Sheamus