Adapts a dropper top sold for 1 oz "regular" bottles to fit on bottles with a smaller mouth. See article for details: http://swampcastle.blogspot.com/2011/12/dropper-caps-for-extract-bottles.html

Also available at Shapeways, sadly not cheaply: http://www.shapeways.com/shops/swampcastle?section=Cooking

Print cap, purchase dropper set: http://www.kingarthurflour.com/shop/items/dropper-caps-sized-for-1-ounce-bottles#none
Pull dropper out of original cap, and pull/twist into printed cap. Droppers now fit smaller mouth bottles.