There should be a workaround for this, but it's not ideal. The ideal solution would be a custom coded module.
If you post out Gift Certificates to people and you charge postage on them, even if only a nominal amount, then set them up as normal Products, and give them a weight. Then when you receive the order set up a Discount Coupon and insert the number of it into the printed Gift Certificate and post that off to the buyer. Make sure it it set for single customer, single use. They can then use the Gift Certificate online (albeit as a Discount Coupon).
Vger



