Receiver hitch?
Do you have a receiver for a hitch? I have a receiver on the rear, and INTEND to put on on the front (for both spot hitches and occasional winch use). There are many carriers made to mount in receivers. I made one for my motorcycle. In my case, I included a female receiver in the carrier, so I can still use a light trailer while the carrier is in use. You might be able to fabricate a carrier that will do the job when you need it, then "unplug" from the receiver when you want to get at the tailgate.
Many SUV's, including Cherokees and such, use swing-away carriers that often hold both a spare tire and a gas can.
In the absence of a receiver, you might come up with something that bolts onto the bumper, but incorporates a hinge or quick-removal pins so you can access the tailgate.
Similar carriers are possible in front, but beware of blocking air flow to the radiator. And be aware of lights on both ends.