[support] Open Text for Purchasers Only

I have a CCK node type which is purchaseable. What I would like to add is the ability for users who are actually purchasing the object to be able to attach a note in a textarea. I want to allow them to add one note per item. I suppose this would be best as part of the checkout process. Any ideas on how I could go about this? I already asked the ecommerce list but no one responded. :( Thanks!