Shipping Option only Available with Coupon Code

Hi

I am using OC 1.5.5.1 and all is going well so far. I have a requirement to give customers the option to collect their purchase from a local exhibition between certain dates/times.

Ideally, when a customer uses a coupon code they will receive a small discount and then see the option "Collect from X" in the delivery options section of the checkout (it would be free to collect the order). I do not want other customers (without a coupon code) to see the option to collect.

I have tried using Beurs http://www.opencart.com/index.php?route ... on_id=1028 to set up the local exhibition shipping option, but nothing shows in the checkout. I am struggling with the manual as it is all in Dutch.

Perhaps a "Collect from Store" type module will work. However, what I need to understand is whether it is possible to activate a shipping module on the back of a coupon code? Without it showing when the code is not used.

Any help appreciated!