That type of mod works well for a WSM, but those are in a container with intake vents. The ECB is built a bunch different. Controling the air flow from the exhaust vent is not recommended.
Some charcoal bowls came with a 3/4 inch hole in the center, some were solid. My original had a hole, I didn't take care of it and it rusted out. Currentlt a ragged 3 inch dia. I found another whole unit on a buy/sell/trade/page on facebook for $10. It was like new, missing one grate. Score !! Charcoal bowl had the hole. I say this because I'm afraid you may need to start over with the holes. I see them on Craigs list and other places all the time from free/curb alert to +$50. Just gotta keep your eyes open. You may be able to use a water bowl for the charcoal. My originals were identical except for the hole.
I cut a peice of expanded steel a little bigger than the bottom of the bowl, so it won't sit all the way to the bottom and provide air flow to coals, also allows ash to fall thru. Added to that an upright contraption (also expanded steel) to provide a gap in the coals. Think a pie with one peice missing. Filled pan with charcoal briquets (except for wedge) and lit one end. It burned for 6 hrs and held steady on 275 deg. All this with the original 3/4 inch hole.
Next I will rig up a slider to cover the hole to choke the temps down even more. I think I will patch the rusted out pan with a plate that has a much larger hole and slider.
I just bought a MES and really have no reason to continue messing with the ECB but I can't stand to give up or see yet another project go unfinished. I have unique ideas for the top vent and need to see how well it works. Working in a machineshop has it's perks.
Start looking for a good charcoal/water bowl and lets start from there.