Eko - Front and rear tie-downs should always be overkill backup tiedowns. The straps that hold the body of the kayak should be the ones that are tight.
The fore and aft tiedowns are really just emergency straps. Just take a line (I like thick nylon rope) from the forward point of your kayak(s) and run it up to the front of the truck, over the hood, up under the plastic bumper cover. If you get down on the ground and look up behind the bumper cover, you'll see plenty of slots in the metal subframe of the KJ. Just put the rope up into one of those slots, down through another slot, then tie it off.
The rear rope is also emergency strapping. I take a rope from the rearmost point on my canoe and run it down to my rear hitch. But you can just just run it through the spare tire. That would work just fine. This is simply a strap the would keep your boat from launching like a missle if you ran into something while driving.
As a caution: Do not overtighten these lines!! You can EASILY round your kayak by doing so.