In other news, Universe Sandbox appears to confirm that a Hot Jupiter setup isn't at all implausible. I constructed a gas giant with 1.25 Jupiter's mass and sent it around the sun at 1.05 AU. Around the gas giant I sent an Earth-like moon with a 10,000 km radius, which had a Charon-sized moon of its own, and, further out, a second gas giant (about half the size of Neptune) orbiting the bigger one. All orbits were stable.

(It MAY be a bitch for spacecraft, depending- Charon orbited the Earth every four and a half hours. You could probably get some hella nice gravity slingshots, though?)

Also, I have no idea how Universe Sandbox calculates temperature for moons. Hot Jupiter is about -10 degrees Celsius; Neptune-moon is about 55 degrees.