Putting esm-ifying aside for a moment. Regarding your underlying issue, what exactly happens when you try and place another ref in your cell?...Nothing happens?...A warning message?
I think I remember somebody mentioning about there being a ref limit, but it's around the 1000 mark (In fact I think this was brought up recently, was it AJV's thread?). But i doubt you've got more then a thousand refs in one cell and saying it looks bland

- Hypno
Edit: yep it was his thread. But if you look through the discussion some talk about being well over the grand limit with no problems
Now I'm curious how many objects I've been blindly placing in my cells...
http://www.gamesas.com/topic/1412392-how-to-tell-how-many-objects-are-in-my-cell-keeping-below-1000/