CJ Fuel
I think you will struggle to find anyone who offers a "temporary" ferry tank for any model of CJ, because there's simply no demand for it. Since you can get from pretty much any one point on the planet to any other point without needing one - by simply going a slightly longer route and stopping for gas - there's no commercial benefit in developing a ferry solution.
In answer to your other point, our operation often ends up positioning between two airports 40 miles apart. If the weather is CAVOK at both airports, and we've copied the destination ATIS before we even start engines, and there's nothing negative being reported, and there are no delays, we will launch with as little as 1100 pounds of fuel - but we do feel a bit like we are living on the edge as we do it, and we would never do that with passengers.
But, in the words of the proverb about old pilots and bold pilots - I'm old!