Remove POST Shipping Method if ANY item in the CART has 0 weight value?

I have products in my Shopping Cart that require separate FREIGHT calculations, as they are too big to be sent via POST and I use COURIERS.... and in the case where someone purchases one of these items, it only allows STORE PICKUP (with instructions about the COURIER charges, etc)....
(this is done by specifying "0" in the weight details of the item, therefore the AUSPOST calculator fails and only allows WALK IN as the option).

BUT...

if the customer purchases ANOTHER item in the same order, which DOES allow POST option, then it only calculates the postage for the 1 item, and allows the order to go through with no indication that the LARGER item cannot be posted!!!

So, is there a way I can STOP items with "0" weight being added to a cart that already has items WITH a weight assigned? (and vice-verca)..... or a way I can DISABLE the POST option if an item with "0" weight is in the cart?

Thanks
Ross.

In the modules, the $this->enabled when true allows it to run and when false it is disabled or hidden ...

You could test for how many products are in the cart with a products_weight of 0 and if 1 or more then disable the module ...