Adding Auto-Refill Filament to AMS While Print in Progress

I'm currently printing a model in grey BL PLA and there isn't going to be enough PLA on the roll to finish it. So no problem I think, I just stick a new roll in an empty slot in my AMS. Except because there's a print in progress, the AMS won't read the RFID tag on the roll, and it won't let me input it manually. So how do I tell the 'system' there's a roll of identical filament in Slot 1 that it can automatically switch to when the existing roll runs out?