What if you build a shelf behind the sign (5' off ground) so you can place both foggers on it. Though, you may not have enough room to have chillers for both either. I am not quite clear on the design yet, perhaps you can use photoshop or some other program to draw a rough idea of how it will work and how you currently are thinking of running the pvc pipe. If you just ran two foggers, both firing behind the sign (on a shelf like I said), outwards towards the colums, and used 90 degree bend pvc tubing to fire them down, the fog would at least come out down over the pillars. The problem then is, how do you chill it fast enough to get it to flow down over the pillars. One idea is using 400 watt foggers, if you have the ability to time it so it uses more of a continuous output (so that you can avoid the 5 minute or so reheat cycle every so often), then the volume of the output will be a lot less, so you might be able to put a little bit of length between the fogger output and the 90 degree bend over each pillar and pack it with dry ice. With a small enough volume out of each fogger, and dry ice with a good foot or so, you might be able to achieve the fog trickling down the pillars.
Unless I am not quite clear on what you are trying to do.