I think that you'll find that the AUC warranty doesn't cover discs and pads as they are classed as consumables along with things like the battery, tyres, wiper blades etc.
My car is also still under AUC and, as I understand it, unlike servicing, you're not expected to have consumables replaced at a BMW dealership and you're free to do so as and when required - so I'd just replace the pads yourself before your I2