structured description

Hi Invoice Ninja, I just discoverd your system and am very thrilled. Already using it for my clients !
My question:

In EU, Belgium, we need to be able to add a structured description to an invoice.
Like
+++123/1234/12345+++

This is a control number. And also when payed by banking account it can be debited by the accounting system.
Is this possible in I-N ?

Maybe you could use a custom field?