This may be common knowledge for some but i just learned it. When entering in one of the instances on Kashyyyk, have your vehicle out, click on the door to enter, then hop on your vehicle before you go in. you will be able to ride your barc, swoop, av-21, etc. in all special instances. I have tried it out and it works so I hope it helps.
This usually works when there's a bit of lag. You'll have to work it a few times to get it down. Once you get attacked by a spawn in the ryatt/madryll(you'll be running as fast as a swoop, not actually on a swoop) you'll slow down to normal speed.