I suppose it depends on where and how long you need to carry it. You might be able to get away with resting it on a foam pad right on the roof, lash it to one of the rack side rails, and tie it off front and back.
(standard disclaimer: If you try that and its not adequate and causes any problems, it's not my fault)
I carried a 17' canoe on my 03, but I had the cross bars.
viewtopic.php?f=33&t=9177" onclick="window.open(this.href);return false; I tied it to the cross rails, up front ran ropes to the anchor hooks underneath. For the back, I bought some bolts to fit the trailer hitch mounting holes and used them to hold some hooks, for tie offs.
Haven't carried the canoe on the Vibe for a while, but I've carried a 14' kayak, pretty much the same setup, except by now I have a trailer hitch, so I tie to that in the back.
A good idea to be wary of sand from the boat getting between the boat and the roof, scratching the paint.
viewtopic.php?f=46&t=43346" onclick="window.open(this.href);return false; currently indicates some roof rack cross rails for sale, no idea on cost/shipping