MPB for slotted PhC waveguide

Dear Steven and others,
I need to calculate the band diagram for the slotted photonic crystal 
waveguide by forming air holes through the silicon nitride slab with 
silicon dioxide along the sides. So it's symmetric slab. Since I need to 
form a two symmetric modes along the center air slot, the center line 
defect does not have to be single line defect as in the MPB examples. I 
already verified the idea by FDTD (meep) by choosing appropriate center 
line defect width and the slot width only for waveguide with short size. 
However it's not a propagating mode. There is strong reflection for the 
structure. Even my application is not to transport light over long 
distance. I still want to output the band diagram to find the guided mode.
So the problem is how do I write the code for the varying center line 
defect not necessarily a single line size.
Thank you.
Best,

LW