More than one attachement

I love so much that the moment that I saw I could help (and get a great extra feature) by registering for the attachments extension at the cost of USD20 I did so immediately. It is the sort of accounting software I was always looking for. One thing I really miss is the opportunity to add more than one attachment per invoice. Why only one? I need one for the invoice I received, one for the payment slip, and sometimes even another one for the contract signed that gave origin to that invoice. Each one is generated at a different time, so the option of keep on upgrading a pdf file with new documents so that it is only one file is not really feasible.

Would it be possible to have this option?