Search the internet for food-grade silicone plugs. Maybe even ebay. Then find some that are bigger than the airflow holes on the deck and sculpt them with an exacto knife so they fit into the airflow holes nice and snug on the side of the deck that you won't be installing the coil.
You'll then have to do the same with the wick ports on that side of the RTA.
That's all I can think of - I have thought about doing this to a dual coil RTA that I have, but I have yet to get around to it.
I found
this site a while ago that sells all kinds of silicone plugs, but I have no idea if they are food grade and I also have no idea if they are a trustworthy company. The quantity per item is also high - I guess they cater to industrial and commercial customers.