If it is a prolapse then you need to give him a warm
bath in sugar water for 20-30 minutes. That will help with the inflammation and it should be able to retract inside the cloaca again.
If that doesn't work you can gently try putting it back in the vent with a cu-tip. This is only after a good 20-30 minute soak in concentrated sugar water. (i had to do this multiple times and it can be stressful for you and the dragon so be careful) Don't shove it, gently make a little room on the side of the vent and it should retract. This should be a last resort kind of thing though.
IF this happens more than once, you need to get it to a vet. If there is blood or the tissue is turning black, take it to the vet.
If you can get the upload to work, can you use imgr, google+ or some other picture hosting site to show the tissue?