I'd just add it or send a separate Paypal invoice.
I get requests like that all the time - there's no problem unless you de-list the product to sell off ebay.
-------------------------------------------------------------------
Every day, a businessperson has to ask himself 2 questions;
Am I being paranoid? and
Am I being paranoid
enough?
Imagination will often carry us to worlds that never were. But without it we go nowhere. Carl Sagan