Hey michels, Lyle told me to call him an idiot and give you the right answer, but I don't think I need to be so harsh. It's just the code was somewhat in transition last I worked on it.
Basically, it's all extensible as is. In this case you'd use the tables API (TAPIr) in a custom module to add a column to the cart view table w/ hook_table_alter(). I don't think the TAPIr docs have been reposted yet, but let me know if this is within your skill to do and I'll post them as soon as I can.