well, there could be a few ways to do this....i took a moment and had a good look at your set up, from your lights, up. i see that you have one cord coming down the middle. That makes this alot easier. What I have found, as stated, CFLs do heat up somewhat. Whatever material you decide to go with, make sure it is light....bristol board from the cheap-o store works well... Myself, i'd measure it up, cut my self two even pieces to slide in on top of my lights. cut a little hole in place for your cord. Mylar the side facing lights, naturally, set that aside.....
Next thing to figure out is how to mount it....simple soloution. most hardware stores have puny L brackets. thats all you need. Our 'everything for a dollar store' has these too....you could use tape.....but I wouldn't to mount it....tooo risky unless you really have to.....
you can, however, run a length of tape around your centre hole to secure your hood, if it already has a sturdy mount...just make sure your cord is secured lol..
Now, i know this sounds quite makeshift, and it is. you could most def make something alot prettier and durable, but this more than does the trick. the bottom line is, Less space used, less lost light. Ensure that you have good ventilation, I would even suggest making slits in the hood to vent if needed. Moving this hood is fast, easy, and pretty cheap to replace . My first hand results will always lead me to making a hood. give it a shot.