Like redzaku said, just toss a fake bolt in it. For example, something like this: http://shop.ehobbyasia.com/king-arms...l#.VUfjrPBw1AU
(do some research on what will fit in your gun. That's just the first result off google)
It covers the ejection port area, so that you see the "bolt" rather than the gearbox.
I think that the "T bar" you're referring to is the charging handle. When you pull that with the fake bolt installed, it will move it back, so that you can adjust your hop up.