Very simple, just mount up and find a chair/bench, anything you can right click to sit in, and use it. You will dismount and sit in the chair, but when you get out you will be running at mounted speed. I have tested this with an epic flyer, and you will still only run at 200%. The effect will last as long as you stay in the same "zone" (don't go through a loading screen).
I am only assuming this does not work on live servers, I have not tested it as I believe there are no chairs in places you could be on a mount.
Alot of private servers have obstacle courses that have parts where you have to sit in chair after chair, and that's how I found this.