Redeem several Gift Certificates at once

[schoolboy]

Is it possible to redeem several (more than one) gift certificates at checkout stage? I manage an online shop selling wedding cakes and we want people to be able to buy certificates as gifts, that can then be redeemed against the value of a wedding cake.

If FIVE people buy gift certificates for "Jane Smith", and then Jane Smith comes to our shop to order her wedding cake, how can she redeem the full value of all five gift certificates against the purchase of one cake?

[schoolboy]

I found the solution on other postings - viz: that these are redeemed and added to the recipient's acount upon "redemption". She then tots them all up before making a purchase...