To get my horses to lope with their heads down, lots and lots of circles at a lope. I also take them to the country and let them lope for a LLLOONNNGGG way. If they are fast and excited at first, I just keep them checked just enough to keep them out of a run and let them go. They usually find their pace pretty quick. But if you don't have that kind of room, circles, serpentines, figure 8's, flexing and lots of direction changes should help. :) Good luck.
Just like smrobs said, circles and turns are great. I would like to add it keeps their mind focus in a way. Instead of doing laps around the arena, turns and making stuff interesting really helps keep them focus on you and what you want out of them.
The Parelli Seven Games are going to help you a lot. Groundwork is where it all starts, anyway.
Like already stated, circles are going to be a great idea. You need to teach Blu the importance of impulsion (which is when go equals whoa) and the importance of going on a loose rein. The faster and more anxious he is, the smaller the circle. A circle's consistency will help calm him down. When you feel him relax, go to a bigger circle. Reward the slightest try and change. And if he does anything where you need to bring him back down use one rein to do it, don't pull on both reins. That will only make his tension worse.