It may be possible to design a number of scenarios around gaming on a
gas giant. An issue of Analog last year did the science fact article
about constructing habitats suspended above the Jovian surface. It
described some of the engineering and materials needed as well.
You could use a gas giant as an ultra high population world under such
a circumstance. Granted your players would be a might spooked when they
saw the population code in the UPP. (You could set it to virtually any
letter above 'A' in the alphabet)
I'll see if I can find which issue and post it in a couple of weeks when
I return.
Later,
Allen Waddell