Note: This might also work for other classes, but working 100% with a druid.
Note #2: The only thing similar to this that I found was this post which wasn't the same.
So, a few simple steps:
1. Use Flight Form, I used the 60% one because I'm broke but it could also work with the 280% one. (Thanks for the correction, Zalman)
2. Fly into Dalaran, anywhere you want.
3. Exit Game -> Exit Now.
4. Log back in. As long as you're in the same area you can fly around happily, if you want to change areas just go to them, exit game again and come back.
5. Enjoy!
And ofc, a screenie as proof: