I've never done the bourbon trail so not sure how they handle things in Kentucky. But we toured several of the dozens of malt whiskey distilleries in the Scottish Highlands a couple of summers ago. The DUI laws are MUCH more stringent in Scotland-more than 1 drink can put you over the limit there depending on weight. What they all seem to do is to provide a "driver's pack" of small mini's for paying guests on their tours. Fortunately, my wife doesn't like scotch, so I got my tasting and then got her driver's pack later, so it worked out double for me!
If I ever get back to Kentucky, I might have to stop in at a few.