Accepting Visa gift cards

[TurkeyFish]

PS 1.6

Has anyone found a smooth solution go accepting Visa gift cards? I frequently have customers who have, say, a $100 gift card they want to apply to an order of $500, and pay the remaining $400 with their credit card via the authorize.net module. 

So far I've had to take their payments by emailing them two separate invoices, for $100 and $400, through authorize.net, or taking their info over the phone and entering the transactions manually in the virtual terminal, and then converting their shopping cart to an order. That's too time consuming for me. I'd like something that the customer can do all himself.

Perhaps a module to use two payment methods? That certainly would complicate things. Maybe I need to offer gift certificates for this purpose, so that they can buy one for $100 and use it as a voucher towards their order?