You could say something like "Due to size issues, I am unable to ship the boat through our local carriers and will have to fly to (insert desired destination) and mail it from there" and try and get him to mail you the plane tickets (of course you'll tell him you'll take the ticket amount off of the boat price, which you know he's never going to buy and you're never going to sell to him).
Or you could say "Hey they won't let me ship it as it is, if you can buy one of those nice boat bags the manufacturers make and ship it to me, I'll send you the boat asap."
You could try the "I looked up your info online, turns out we went to high school together/you live next to my parents/bogus personal connection I'll bring it with me when I visit next week and you can give me the cash."
Or go all psycho satanic worshipper, evangelical, member of the mob crazy on 'em.
Oh, the options are endless