Idea 1) If you have plenty of money just ask John at FAOIS to build you one - I don't have that much money personally ;-) I'm sure that will be the most attractive and functional solution.
Idea 2) If you don't want to modify your sump but replace it with something cheap: You could make chambers in a 20 gallon tank for about $40 ... 25$ for the tank and 15 for cheap-o glass at home depot... that's what I did. Ugly but it works.
Idea 3) Cutting it up:
I'm assuming that chamber 3 and 4 are open to each other below the bioball chamber.
If you wanted to make this a typical sump you could :
1) Remove that entire bioball assembly (cut it out if you have to)
2) Cut out the wall separating the top of 3 from 4
3) Re-glue that wall so it's on the bottom and the water flows over the top from 3 to 4 instead of underneath.
4) If the water is crashing down too much still you could cut the top off the wall separating 1 from 3.
Also people usually put baffles (kind of like the 2 walls and the sponge) between the skimmer and the refugium but I don't think you have to.
Here's a bigger picture by the way:
http://a1272.g.akamai.net/7/1272/11...s/Categoryimages/larger/lg_rd_22840_30497.jpg
I don't understand why it not being level in your comment #"c" is a problem.