Title says it all, really. Since their taglines say "you should not have this on you", and placing them doesn't work, I see two options: disable this ability (or make pick-block give normal Dayblooms/Nightshades), or allow them to be placed and add them to the Creative menu (I know, you don't want Survival players obtaining them, but c'mon, it's Creative mode). Personally, I'm in favor of the latter.