These are the two things I saw in DarkSoul's sig:
http://www.aquariacentral.com/forums/showthread.php?t=123794
and
http://www.aquariacentral.com/forums/showthread.php?t=123794
I'm not sure about the exact dimesions of your tank, but I don't think that will work for you. I think you said you have 18" to work with. At most(at most) you could fit 4 CFL's in that space, but probably only 3. Currently, the highest wattage 6500K CFL on the market is 27W. 27 x 4 = 108, or 27 x 3 = 81. Not going to be enough for you. According to the wpg rule, you need at least 110w over a 55g. Due to the restrike of CFL's, the poor reflection quality of any reflector you can DIY, and the depth of a 55g hex, the wpg rule doesn't work(as you know). Therefore, I would call 165w the minimum over that tank.
So, you need 6 27w bulbs = 162W.
Start googling combinations of DIY, HOOD, HEX, CUSTOM, LIGHTING, WATTS, PLANTS,etc....
And read, read everything you see. You may just learn enough to design/build it yourself.
Eventually, you will find a plan for a hex hood. I've seen one, but I don't have the time to find it now.
Again, this is all only relevant if you want to add ferts, co2, and lighthing all at the same time.