Add blank lines and attached file to invoice

Does anyone have a suggestion or workaround how to add blank lines (of a not existing product) to an invoice? Very usefull when adding for example extra services, printing or handling costs to an invoice. We first added them as items in the catalog. But then they show up on the public front of the store.

Second nifty feature would be an upload file possibility to an invoice and/or communication area (like extra PDF or other terms). Also Q&D workarounds are welcome! :wink: