I'm sure this issue is long settled, but something that worked for me was buying one of those nylon skateboard bags from eBay and sticking it in there. When it's just a skateboard, they're like "What the hell are you doing with this here?! You need to check this for $50!" When it's in a bag, the same people (who, remember, see literally tens of thousands of bags a day) don't seem to even notice.