@lpwilliams Just been looking at one of the examples in your idea...
B)> I have £100 cashback and chose Amazon vouchers (to give me an extra 3%) IF giffgaff can bulk buy vouchers through corporate scheme at a 10% reduction, then cost to giffgaff = £90 and I get £103. I have more and giffgaff saved too - WIN:WIN
Is the £103 you get £103 in Amazon vouchers? If so then isn't the cost to giffgaff £103 - 10% = £92.70p? Or am I confusing myself some where?
Either way... nice idea.