Recording unique voucher codes - and then searching for them

Hi

We are looking at running a promotion through one of the group buying sites (such as Groupon or Keynoir) and I have a worry about it.

Basically, the customer is issued with a voucher which contains a voucher code, they then call the box office to redeem their voucher for a ticket. The customer can purchase more than one voucher, all of which have a unique ID. I would like some way of searching to see if the code has already been used, and then recording it on the customer's account. Unfortunately we do not get the customer's details and associated voucher code in advance of them calling us.

I've thought about using Attributes as these are eary to search on, but it seems you can't free type into the Attribute Value cell, just pre-fill the T_KWCODED_VALUES table to select from a drop down. This is not workable for us. Please do correct me if I'm wrong.

I've also thought about creating a custom tab but as far as I can tell, there's no way to search these from the Constituent search screen. Again, please correct me if I'm wrong.

I did consider creating a report that allows searching for the voucher code, but I feel this would be too time consuming for the box office at point of sale.

Can anyone think of a way to do this that allows for searching and free-typing, and is not going to be time-consuming for the box office?

Thanks

Siobhan