You can simulate it. Just find a normal AI airliner, fly up close underneith, and loiter there for a few minutes. Then reload the airplane model or edit the fuel load.
I don't think actual mid air refuel is possible in MSFS.
There's a command for filling the fuel tanks in FS9. Go to the keyboard controls, it'll be in there - I think it's disabled by default, if so assign it as Shift-F or something like that, or a joystick button if you prefer.