Upload & Sell: Off
You can apply those settings in the "Apply during import" section in the import screen using the "Metadata" setting. Just create a profile there and make sure you check the "keywords" option and leave it blank.
Haven't tested myself but I'm pretty confident this should do the trick!
Another thing you perhaps know already is you can purge your unused keywords quite easily by going to "Metadata -> Purge unused keywords" in the menu bar of LR.