I think the consensus of previous posts is that you have to physically remove the Wifi/Bluetooth card. Just disabling the drivers won't do.
You obviously replace the card after completing the upgrade, and anyway need to be connected by ethernet cable while the card is out of the machine, so there should not be any difficulty in then downloading the new drivers.
Since one is going to this amount of trouble anyway, made me wonder whether there might be any benefit in upgrading the card at the same time - they are not exactly expensive - or is the HP BIOS whitelisted to prevent this? Does anybody know?