Gift card work around, paying invoices

I’m having trouble with
making best use of gift cards without creating a bunch more work for myself

What I’m trying to do
family members have bought gift cards for kids who want to come to events like summer camp BUT if a parent has already paid the deposit, they can’t use gift cards to pay the invoice. am trying to find a work around. I could create a new invoice, manually check how much the student has been sent in gift cards, manually discount them from the invoice and send with new balance total, but then how do I mark in the gift card manager how much has been spent?

Thanks